Stateful connection resets

ABSTRACT

A method of resetting a stateful connection in a storage cluster with stateless load-balancing is provided. The method includes receiving a packet associated with a stateful connection between a client and a first storage node of the storage cluster. The method includes sending a reset packet from a second storage node to the client, through a stateless load balancer, responsive to the second storage node failing to recognize the packet associated with the stateful connection between the client and the first storage node, wherein the client resets the stateful connection responsive to receiving the reset packet. The method includes sending further reset packets from the load balancer to a plurality of storage nodes of the storage cluster, responsive to receiving, at the load balancer, the reset packet from the second storage node, wherein the plurality of storage nodes reset stateful connection information responsive to receiving the further reset packets.

BACKGROUND

Transmission control protocol (TCP) is a stateful protocol that supportsendpoints on a network establishing a TCP connection, communicatingthrough the TCP connection, and ultimately terminating the TCPconnection. Both endpoints, e.g., two computers, or a client and aserver, maintain state information about the TCP connection.Communication nodes on the network between the client and server may bestateful or stateless. Many computing, communication and storage systemswith multiple servers or nodes use load-balancing to distributecommunication, workloads and/or data across the multiple servers ornodes. The load-balancing can also be stateful or stateless. A problemarises when the server or node membership in one of these computing,communication or storage systems changes, affecting statelessload-balancing, and packets associated with a TCP connection aredelivered to a different server or node than the one for which the TCPconnection was originally established. Under these circumstances, anapplication that is not receiving a response may timeout, but this islikely on the order of minutes later, rather than milliseconds oflatency, which is more desirable. A stateful load balancer may notexperience this problem, but the stateful load balancer requirestracking of states of TCP connections with attendant consumption ofmemory and processing resources and thus does not scale well for largersystems with more servers or nodes and/or more clients. This problem isespecially critical in a storage cluster with an expandable number ofstorage nodes and other features for scaling the capacity of the storagesystem, where stateless load-balancing is a desired feature for scalablesystem architecture. Therefore, there is a need in the art for asolution which overcomes the drawbacks described above.

SUMMARY

In some embodiments, a method of resetting a stateful connection in astorage cluster with stateless load-balancing is provided. The methodincludes receiving a packet associated with a stateful connectionbetween a client and a first storage node of the storage cluster. Themethod includes sending a reset packet from a second storage node to theclient, through a stateless load balancer, responsive to the secondstorage node failing to recognize the packet associated with thestateful connection between the client and the first storage node,wherein the client resets the stateful connection responsive toreceiving the reset packet. The method includes sending further resetpackets from the stateless load balancer to a plurality of storage nodesof the storage cluster, responsive to receiving, at the stateless loadbalancer, the reset packet from the second storage node, wherein theplurality of storage nodes reset stateful connection informationresponsive to receiving the further reset packets. The method may beembodied as executable instructions on a computer readable medium and asa storage system configured to execute the method.

Other aspects and advantages of the embodiments will become apparentfrom the following detailed description taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments and the advantages thereof may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings. These drawings in no waylimit any changes in form and detail that may be made to the describedembodiments by one skilled in the art without departing from the spiritand scope of the described embodiments.

The present disclosure is illustrated by way of example, and not by wayof limitation, and can be more fully understood with reference to thefollowing detailed description when considered in connection with thefigures as described below.

FIG. 1A illustrates a first example system for data storage inaccordance with some implementations.

FIG. 1B illustrates a second example system for data storage inaccordance with some implementations.

FIG. 1C illustrates a third example system for data storage inaccordance with some implementations.

FIG. 1D illustrates a fourth example system for data storage inaccordance with some implementations.

FIG. 2A is a perspective view of a storage cluster with multiple storagenodes and internal storage coupled to each storage node to providenetwork attached storage, in accordance with some embodiments.

FIG. 2B is a block diagram showing an interconnect switch couplingmultiple storage nodes in accordance with some embodiments.

FIG. 2C is a multiple level block diagram, showing contents of a storagenode and contents of one of the non-volatile solid state storage unitsin accordance with some embodiments.

FIG. 2D shows a storage server environment, which uses embodiments ofthe storage nodes and storage units of FIGS. 1-3 in accordance with someembodiments.

FIG. 2E is a blade hardware block diagram, showing a control plane,compute and storage planes, and authorities interacting with underlyingphysical resources, in accordance with some embodiments.

FIG. 2F depicts elasticity software layers in blades of a storagecluster, in accordance with some embodiments.

FIG. 2G depicts authorities and storage resources in blades of a storagecluster, in accordance with some embodiments.

FIG. 3A sets forth a diagram of a storage system that is coupled fordata communications with a cloud services provider in accordance withsome embodiments of the present disclosure.

FIG. 3B sets forth a diagram of a storage system in accordance with someembodiments of the present disclosure.

FIG. 4 is a block diagram of a stateless load balancer for embodimentsof a storage cluster such as shown in FIGS. 2A-3B in accordance withsome embodiments.

FIG. 5 illustrates a TCP (transmission control protocol) connectionestablished between a client and a storage node of a storage cluster,and a scenario when a stateless load balancer sends a packet associatedwith the TCP connection to another storage node in accordance with someembodiments.

FIG. 6 illustrates the storage node sending out a TCP reset packet, in asolution to the problem depicted in FIG. 5 in accordance with someembodiments.

FIG. 7 depicts internal processes in a storage node receiving a TCPreset packet in accordance with some embodiments.

FIG. 8 illustrates the storage node sending out a TCP reset packet, in amulti-chassis storage cluster solution to the problem depicted in FIG. 5in accordance with some embodiments.

FIG. 9 is a flow diagram of a method of resetting a stateful connectionin a storage cluster with stateless load-balancing, which can bepracticed by embodiments of storage clusters as described herein, andfurther storage clusters and storage systems in accordance with someembodiments.

FIG. 10 is an illustration showing an exemplary computing device whichmay implement the embodiments described herein.

DETAILED DESCRIPTION

Some embodiments of storage systems described herein have statelessload-balancing, and a mechanism for resetting TCP (transmission controlprotocol) connections when a packet that should belong to a TCPconnection established by one storage node is delivered to anotherstorage node, as a result of changing membership of storage nodes in astorage cluster. The storage node that receives the packet, but does notrecognize the packet because this storage node is not the one that ownsthe TCP connection, sends a TCP reset packet to the client. A statelessload balancer, which does not maintain state information about TCPconnections, traps the TCP reset packet and sends more TCP resetpackets, to the storage nodes (except the storage node that sent to theTCP reset packet, in some embodiments). Storage nodes receiving such TCPreset packets, and the client receiving the TCP reset packet, reset theTCP connection information. This mechanism scales well with largerstorage clusters, including multi-chassis storage clusters, and does notrequire stateful load-balancing. Storage arrays with storage controllersare described below with reference to FIGS. 1A-1D, storage clusters withstorage nodes and blades are described with reference to FIGS. 2A-3B,and storage clusters with stateless load-balancing and the TCP resetmechanism are described with reference to FIGS. 4-9.

FIG. 1A illustrates an example system for data storage, in accordancewith some implementations. System 100 (also referred to as “storagesystem” herein) includes numerous elements for purposes of illustrationrather than limitation. It may be noted that system 100 may include thesame, more, or fewer elements configured in the same or different mannerin other implementations.

System 100 includes a number of computing devices 164. Computing devices(also referred to as “client devices” herein) may be for example, aserver in a data center, a workstation, a personal computer, a notebook,or the like. Computing devices 164 are coupled for data communicationsto one or more storage arrays 102 through a storage area network (SAN)158 or a local area network (LAN) 160.

The SAN 158 may be implemented with a variety of data communicationsfabrics, devices, and protocols. For example, the fabrics for SAN 158may include Fibre Channel, Ethernet, Infiniband, Serial Attached SmallComputer System Interface (SAS), or the like. Data communicationsprotocols for use with SAN 158 may include Advanced TechnologyAttachment (ATA), Fibre Channel Protocol, Small Computer SystemInterface (SCSI), Internet Small Computer System Interface (iSCSI),HyperSCSI, Non-Volatile Memory Express (NVMe) over Fabrics, or the like.It may be noted that SAN 158 is provided for illustration, rather thanlimitation. Other data communication couplings may be implementedbetween computing devices 164 and storage arrays 102.

The LAN 160 may also be implemented with a variety of fabrics, devices,and protocols. For example, the fabrics for LAN 160 may include Ethernet(802.3), wireless (802.11), or the like. Data communication protocolsfor use in LAN 160 may include Transmission Control Protocol (TCP), UserDatagram Protocol (UDP), Internet Protocol (IP), HyperText TransferProtocol (HTTP), Wireless Access Protocol (WAP), Handheld DeviceTransport Protocol (HDTP), Session Initiation Protocol (SIP), Real TimeProtocol (RTP), or the like.

Storage arrays 102 may provide persistent data storage for the computingdevices 164. Storage array 102A may be contained in a chassis (notshown), and storage array 102B may be contained in another chassis (notshown), in implementations. Storage array 102A and 102B may include oneor more storage array controllers 110 (also referred to as “controller”herein). A storage array controller 110 may be embodied as a module ofautomated computing machinery comprising computer hardware, computersoftware, or a combination of computer hardware and software. In someimplementations, the storage array controllers 110 may be configured tocarry out various storage tasks. Storage tasks may include writing datareceived from the computing devices 164 to storage array 102, erasingdata from storage array 102, retrieving data from storage array 102 andproviding data to computing devices 164, monitoring and reporting ofdisk utilization and performance, performing redundancy operations, suchas Redundant Array of Independent Drives (RAID) or RAID-like dataredundancy operations, compressing data, encrypting data, and so forth.

Storage array controller 110 may be implemented in a variety of ways,including as a Field Programmable Gate Array (FPGA), a ProgrammableLogic Chip (PLC), an Application Specific Integrated Circuit (ASIC),System-on-Chip (SOC), or any computing device that includes discretecomponents such as a processing device, central processing unit,computer memory, or various adapters. Storage array controller 110 mayinclude, for example, a data communications adapter configured tosupport communications via the SAN 158 or LAN 160. In someimplementations, storage array controller 110 may be independentlycoupled to the LAN 160. In implementations, storage array controller 110may include an I/O controller or the like that couples the storage arraycontroller 110 for data communications, through a midplane (not shown),to a persistent storage resource 170 (also referred to as a “storageresource” herein). The persistent storage resource 170 main include anynumber of storage drives 171 (also referred to as “storage devices”herein) and any number of non-volatile Random Access Memory (NVRAM)devices (not shown).

In some implementations, the NVRAM devices of a persistent storageresource 170 may be configured to receive, from the storage arraycontroller 110, data to be stored in the storage drives 171. In someexamples, the data may originate from computing devices 164. In someexamples, writing data to the NVRAM device may be carried out morequickly than directly writing data to the storage drive 171. Inimplementations, the storage array controller 110 may be configured toutilize the NVRAM devices as a quickly accessible buffer for datadestined to be written to the storage drives 171. Latency for writerequests using NVRAM devices as a buffer may be improved relative to asystem in which a storage array controller 110 writes data directly tothe storage drives 171. In some implementations, the NVRAM devices maybe implemented with computer memory in the form of high bandwidth, lowlatency RAM. The NVRAM device is referred to as “non-volatile” becausethe NVRAM device may receive or include a unique power source thatmaintains the state of the RAM after main power loss to the NVRAMdevice. Such a power source may be a battery, one or more capacitors, orthe like. In response to a power loss, the NVRAM device may beconfigured to write the contents of the RAM to a persistent storage,such as the storage drives 171.

In implementations, storage drive 171 may refer to any device configuredto record data persistently, where “persistently” or “persistent” refersas to a device's ability to maintain recorded data after loss of power.In some implementations, storage drive 171 may correspond to non-diskstorage media. For example, the storage drive 171 may be one or moresolid-state drives (SSDs), flash memory based storage, any type ofsolid-state non-volatile memory, or any other type of non-mechanicalstorage device. In other implementations, storage drive 171 may includemay include mechanical or spinning hard disk, such as hard-disk drives(HDD).

In some implementations, the storage array controllers 110 may beconfigured for offloading device management responsibilities fromstorage drive 171 in storage array 102. For example, storage arraycontrollers 110 may manage control information that may describe thestate of one or more memory blocks in the storage drives 171. Thecontrol information may indicate, for example, that a particular memoryblock has failed and should no longer be written to, that a particularmemory block contains boot code for a storage array controller 110, thenumber of program-erase (P/E) cycles that have been performed on aparticular memory block, the age of data stored in a particular memoryblock, the type of data that is stored in a particular memory block, andso forth. In some implementations, the control information may be storedwith an associated memory block as metadata. In other implementations,the control information for the storage drives 171 may be stored in oneor more particular memory blocks of the storage drives 171 that areselected by the storage array controller 110. The selected memory blocksmay be tagged with an identifier indicating that the selected memoryblock contains control information. The identifier may be utilized bythe storage array controllers 110 in conjunction with storage drives 171to quickly identify the memory blocks that contain control information.For example, the storage controllers 110 may issue a command to locatememory blocks that contain control information. It may be noted thatcontrol information may be so large that parts of the controlinformation may be stored in multiple locations, that the controlinformation may be stored in multiple locations for purposes ofredundancy, for example, or that the control information may otherwisebe distributed across multiple memory blocks in the storage drive 171.

In implementations, storage array controllers 110 may offload devicemanagement responsibilities from storage drives 171 of storage array 102by retrieving, from the storage drives 171, control informationdescribing the state of one or more memory blocks in the storage drives171. Retrieving the control information from the storage drives 171 maybe carried out, for example, by the storage array controller 110querying the storage drives 171 for the location of control informationfor a particular storage drive 171. The storage drives 171 may beconfigured to execute instructions that enable the storage drive 171 toidentify the location of the control information. The instructions maybe executed by a controller (not shown) associated with or otherwiselocated on the storage drive 171 and may cause the storage drive 171 toscan a portion of each memory block to identify the memory blocks thatstore control information for the storage drives 171. The storage drives171 may respond by sending a response message to the storage arraycontroller 110 that includes the location of control information for thestorage drive 171. Responsive to receiving the response message, storagearray controllers 110 may issue a request to read data stored at theaddress associated with the location of control information for thestorage drives 171.

In other implementations, the storage array controllers 110 may furtheroffload device management responsibilities from storage drives 171 byperforming, in response to receiving the control information, a storagedrive management operation. A storage drive management operation mayinclude, for example, an operation that is typically performed by thestorage drive 171 (e.g., the controller (not shown) associated with aparticular storage drive 171). A storage drive management operation mayinclude, for example, ensuring that data is not written to failed memoryblocks within the storage drive 171, ensuring that data is written tomemory blocks within the storage drive 171 in such a way that adequatewear leveling is achieved, and so forth.

In implementations, storage array 102 may implement two or more storagearray controllers 110. For example, storage array 102A may includestorage array controllers 110A and storage array controllers 110B. At agiven instance, a single storage array controller 110 (e.g., storagearray controller 110A) of a storage system 100 may be designated withprimary status (also referred to as “primary controller” herein), andother storage array controllers 110 (e.g., storage array controller110A) may be designated with secondary status (also referred to as“secondary controller” herein). The primary controller may haveparticular rights, such as permission to alter data in persistentstorage resource 170 (e.g., writing data to persistent storage resource170). At least some of the rights of the primary controller maysupersede the rights of the secondary controller. For instance, thesecondary controller may not have permission to alter data in persistentstorage resource 170 when the primary controller has the right. Thestatus of storage array controllers 110 may change. For example, storagearray controller 110A may be designated with secondary status, andstorage array controller 110B may be designated with primary status.

In some implementations, a primary controller, such as storage arraycontroller 110A, may serve as the primary controller for one or morestorage arrays 102, and a second controller, such as storage arraycontroller 110B, may serve as the secondary controller for the one ormore storage arrays 102. For example, storage array controller 110A maybe the primary controller for storage array 102A and storage array 102B,and storage array controller 110B may be the secondary controller forstorage array 102A and 102B. In some implementations, storage arraycontrollers 110C and 110D (also referred to as “storage processingmodules”) may neither have primary or secondary status. Storage arraycontrollers 110C and 110D, implemented as storage processing modules,may act as a communication interface between the primary and secondarycontrollers (e.g., storage array controllers 110A and 110B,respectively) and storage array 102B. For example, storage arraycontroller 110A of storage array 102A may send a write request, via SAN158, to storage array 102B. The write request may be received by bothstorage array controllers 110C and 110D of storage array 102B. Storagearray controllers 110C and 110D facilitate the communication, e.g., sendthe write request to the appropriate storage drive 171. It may be notedthat in some implementations storage processing modules may be used toincrease the number of storage drives controlled by the primary andsecondary controllers.

In implementations, storage array controllers 110 are communicativelycoupled, via a midplane (not shown), to one or more storage drives 171and to one or more NVRAM devices (not shown) that are included as partof a storage array 102. The storage array controllers 110 may be coupledto the midplane via one or more data communication links and themidplane may be coupled to the storage drives 171 and the NVRAM devicesvia one or more data communications links. The data communications linksdescribed herein are collectively illustrated by data communicationslinks 108 and may include a Peripheral Component Interconnect Express(PCIe) bus, for example.

FIG. 1B illustrates an example system for data storage, in accordancewith some implementations. Storage array controller 101 illustrated inFIG. 1B may similar to the storage array controllers 110 described withrespect to FIG. 1A. In one example, storage array controller 101 may besimilar to storage array controller 110A or storage array controller110B. Storage array controller 101 includes numerous elements forpurposes of illustration rather than limitation. It may be noted thatstorage array controller 101 may include the same, more, or fewerelements configured in the same or different manner in otherimplementations. It may be noted that elements of FIG. 1A may beincluded below to help illustrate features of storage array controller101.

Storage array controller 101 may include one or more processing devices104 and random access memory (RAM) 111. Processing device 104 (orcontroller 101) represents one or more general-purpose processingdevices such as a microprocessor, central processing unit, or the like.More particularly, the processing device 104 (or controller 101) may bea complex instruction set computing (CISC) microprocessor, reducedinstruction set computing (RISC) microprocessor, very long instructionword (VLIW) microprocessor, or a processor implementing otherinstruction sets or processors implementing a combination of instructionsets. The processing device 104 (or controller 101) may also be one ormore special-purpose processing devices such as an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA), adigital signal processor (DSP), network processor, or the like.

The processing device 104 may be connected to the RAM 111 via a datacommunications link 106, which may be embodied as a high speed memorybus such as a Double-Data Rate 4 (DDR4) bus. Stored in RAM 111 is anoperating system 112. In some implementations, instructions 113 arestored in RAM 111. Instructions 113 may include computer programinstructions for performing operations in in a direct-mapped flashstorage system. In one embodiment, a direct-mapped flash storage systemis one that that addresses data blocks within flash drives directly andwithout an address translation performed by the storage controllers ofthe flash drives.

In implementations, storage array controller 101 includes one or morehost bus adapters 103 that are coupled to the processing device 104 viaa data communications link 105. In implementations, host bus adapters103 may be computer hardware that connects a host system (e.g., thestorage array controller) to other network and storage arrays. In someexamples, host bus adapters 103 may be a Fibre Channel adapter thatenables the storage array controller 101 to connect to a SAN, anEthernet adapter that enables the storage array controller 101 toconnect to a LAN, or the like. Host bus adapters 103 may be coupled tothe processing device 104 via a data communications link 105 such as,for example, a PCIe bus.

In implementations, storage array controller 101 may include a host busadapter 114 that is coupled to an expander 115. The expander 115 may beused to attach a host system to a larger number of storage drives. Theexpander 115 may, for example, be a SAS expander utilized to enable thehost bus adapter 114 to attach to storage drives in an implementationwhere the host bus adapter 114 is embodied as a SAS controller.

In implementations, storage array controller 101 may include a switch116 coupled to the processing device 104 via a data communications link109. The switch 116 may be a computer hardware device that can createmultiple endpoints out of a single endpoint, thereby enabling multipledevices to share a single endpoint. The switch 116 may, for example, bea PCIe switch that is coupled to a PCIe bus (e.g., data communicationslink 109) and presents multiple PCIe connection points to the midplane.

In implementations, storage array controller 101 includes a datacommunications link 107 for coupling the storage array controller 101 toother storage array controllers. In some examples, data communicationslink 107 may be a QuickPath Interconnect (QPI) interconnect.

A traditional storage system that uses traditional flash drives mayimplement a process across the flash drives that are part of thetraditional storage system. For example, a higher level process of thestorage system may initiate and control a process across the flashdrives. However, a flash drive of the traditional storage system mayinclude its own storage controller that also performs the process. Thus,for the traditional storage system, a higher level process (e.g.,initiated by the storage system) and a lower level process (e.g.,initiated by a storage controller of the storage system) may both beperformed.

To resolve various deficiencies of a traditional storage system,operations may be performed by higher level processes and not by thelower level processes. For example, the flash storage system may includeflash drives that do not include storage controllers that provide theprocess. Thus, the operating system of the flash storage system itselfmay initiate and control the process. This may be accomplished by adirect-mapped flash storage system that addresses data blocks within theflash drives directly and without an address translation performed bythe storage controllers of the flash drives.

The operating system of the flash storage system may identify andmaintain a list of allocation units across multiple flash drives of theflash storage system. The allocation units may be entire erase blocks ormultiple erase blocks. The operating system may maintain a map oraddress range that directly maps addresses to erase blocks of the flashdrives of the flash storage system.

Direct mapping to the erase blocks of the flash drives may be used torewrite data and erase data. For example, the operations may beperformed on one or more allocation units that include a first data anda second data where the first data is to be retained and the second datais no longer being used by the flash storage system. The operatingsystem may initiate the process to write the first data to new locationswithin other allocation units and erasing the second data and markingthe allocation units as being available for use for subsequent data.Thus, the process may only be performed by the higher level operatingsystem of the flash storage system without an additional lower levelprocess being performed by controllers of the flash drives.

Advantages of the process being performed only by the operating systemof the flash storage system include increased reliability of the flashdrives of the flash storage system as unnecessary or redundant writeoperations are not being performed during the process. One possiblepoint of novelty here is the concept of initiating and controlling theprocess at the operating system of the flash storage system. Inaddition, the process can be controlled by the operating system acrossmultiple flash drives. This is contrast to the process being performedby a storage controller of a flash drive.

A storage system can consist of two storage array controllers that sharea set of drives for failover purposes, or it could consist of a singlestorage array controller that provides a storage service that utilizesmultiple drives, or it could consist of a distributed network of storagearray controllers each with some number of drives or some amount ofFlash storage where the storage array controllers in the networkcollaborate to provide a complete storage service and collaborate onvarious aspects of a storage service including storage allocation andgarbage collection.

FIG. 1C illustrates a third example system 117 for data storage inaccordance with some implementations. System 117 (also referred to as“storage system” herein) includes numerous elements for purposes ofillustration rather than limitation. It may be noted that system 117 mayinclude the same, more, or fewer elements configured in the same ordifferent manner in other implementations.

In one embodiment, system 117 includes a dual Peripheral ComponentInterconnect (PCI) flash storage device 118 with separately addressablefast write storage. System 117 may include a storage controller 119. Inone embodiment, storage controller 119 may be a CPU, ASIC, FPGA, or anyother circuitry that may implement control structures necessaryaccording to the present disclosure. In one embodiment, system 117includes flash memory devices (e.g., including flash memory devices 120a-n), operatively coupled to various channels of the storage devicecontroller 119. Flash memory devices 120 a-n, may be presented to thecontroller 119 as an addressable collection of Flash pages, eraseblocks, and/or control elements sufficient to allow the storage devicecontroller 119 to program and retrieve various aspects of the Flash. Inone embodiment, storage device controller 119 may perform operations onflash memory devices 120A-N including storing and retrieving datacontent of pages, arranging and erasing any blocks, tracking statisticsrelated to the use and reuse of Flash memory pages, erase blocks, andcells, tracking and predicting error codes and faults within the Flashmemory, controlling voltage levels associated with programming andretrieving contents of Flash cells, etc.

In one embodiment, system 117 may include random access memory (RAM) 121to store separately addressable fast-write data. In one embodiment, RAM121 may be one or more separate discrete devices. In another embodiment,RAM 121 may be integrated into storage device controller 119 or multiplestorage device controllers. The RAM 121 may be utilized for otherpurposes as well, such as temporary program memory for a processingdevice (E.g., a central processing unit (CPU)) in the storage devicecontroller 119.

In one embodiment, system 119 may include a stored energy device 122,such as a rechargeable battery or a capacitor. Stored energy device 122may store energy sufficient to power the storage device controller 119,some amount of the RAM (e.g., RAM 121), and some amount of Flash memory(e.g., Flash memory 120 a-120 n) for sufficient time to write thecontents of RAM to Flash memory. In one embodiment, storage devicecontroller 119 may write the contents of RAM to Flash Memory if thestorage device controller detects loss of external power.

In one embodiment, system 117 includes two data communications links 123a, 123 b. In one embodiment, data communications links 123 a, 123 b maybe PCI interfaces. In another embodiment, data communications links 123a, 123 b may be based on other communications standards (e.g.,HyperTransport, InfiBand, etc.). Data communications links 123 a, 123 bmay be based on non-volatile memory express (NVMe) or NCMe over fabrics(NVMf) specifications that allow external connection to the storagedevice controller 119 from other components in the storage system 117.It should be noted that data communications links may be interchangeablyreferred to herein as PCI buses for convenience.

System 117 may also include an external power source (not shown), whichmay be provided over one or both data communications links 123 a, 123 b,or which may be provided separately. An alternative embodiment includesa separate Flash memory (not shown) dedicated for use in storing thecontent of RAM 121. The storage device controller 119 may present alogical device over a PCI bus which may include an addressablefast-write logical device, or a distinct part of the logical addressspace of the storage device 118, which may be presented as PCI memory oras persistent storage. In one embodiment, operations to store into thedevice are directed into the RAM 121. On power failure, the storagedevice controller 119 may write stored content associated with theaddressable fast-write logical storage to Flash memory (e.g., Flashmemory 120 a-n) for long-term persistent storage.

In one embodiment, the logical device may include some presentation ofsome or all of the content of the Flash memory devices 120 a-n, wherethat presentation allows a storage system including a storage device 118(e.g., storage system 117) to directly address Flash memory pages anddirectly reprogram erase blocks from storage system components that areexternal to the storage device through the PCI bus. The presentation mayalso allow one or more of the external components to control andretrieve other aspects of the Flash memory including some or all of:tracking statistics related to use and reuse of Flash memory pages,erase blocks, and cells across all the Flash memory devices; trackingand predicting error codes and faults within and across the Flash memorydevices; controlling voltage levels associated with programming andretrieving contents of Flash cells; etc.

In one embodiment, the stored energy device 122 may be sufficient toensure completion of in-progress operations to the Flash memory devices107 a-120 n stored energy device 122 may power storage device controller119 and associated Flash memory devices (e.g., 120 a-n) for thoseoperations, as well as for the storing of fast-write RAM to Flashmemory. Stored energy device 122 may be used to store accumulatedstatistics and other parameters kept and tracked by the Flash memorydevices 120 a-n and/or the storage device controller 119. Separatecapacitors or stored energy devices (such as smaller capacitors near orembedded within the Flash memory devices themselves) may be used forsome or all of the operations described herein.

Various schemes may be used to track and optimize the life span of thestored energy component, such as adjusting voltage levels over time,partially discharging the storage energy device 122 to measurecorresponding discharge characteristics, etc. If the available energydecreases over time, the effective available capacity of the addressablefast-write storage may be decreased to ensure that it can be writtensafely based on the currently available stored energy.

FIG. 1D illustrates a third example system 124 for data storage inaccordance with some implementations. In one embodiment, system 124includes storage controllers 125 a, 125 b. In one embodiment, storagecontrollers 125 a, 125 b are operatively coupled to Dual PCI storagedevices 119 a, 119 b and 119 c, 119 d, respectively. Storage controllers125 a, 125 b may be operatively coupled (e.g., via a storage network130) to some number of host computers 127 a-n.

In one embodiment, two storage controllers (e.g., 125 a and 125 b)provide storage services, such as a small computer system interface(SCSI) block storage array, a file server, an object server, a databaseor data analytics service, etc. The storage controllers 125 a, 125 b mayprovide services through some number of network interfaces (e.g., 126a-d) to host computers 127 a-n outside of the storage system 124.Storage controllers 125 a, 125 b may provide integrated services or anapplication entirely within the storage system 124, forming a convergedstorage and compute system. The storage controllers 125 a, 125 b mayutilize the fast write memory within or across storage devices 119 a-dto journal in progress operations to ensure the operations are not loston a power failure, storage controller removal, storage controller orstorage system shutdown, or some fault of one or more software orhardware components within the storage system 124.

In one embodiment, controllers 125 a, 125 b operate as PCI masters toone or the other PCI buses 128 a, 128 b. In another embodiment, 128 aand 128 b may be based on other communications standards (e.g.,HyperTransport, InfiBand, etc.). Other storage system embodiments mayoperate storage controllers 125 a, 125 b as multi-masters for both PCIbuses 128 a, 128 b. Alternately, a PCI/NVMe/NVMf switchinginfrastructure or fabric may connect multiple storage controllers. Somestorage system embodiments may allow storage devices to communicate witheach other directly rather than communicating only with storagecontrollers. In one embodiment, a storage device controller 119 a may beoperable under direction from a storage controller 125 a to synthesizeand transfer data to be stored into Flash memory devices from data thathas been stored in RAM (e.g., RAM 121 of FIG. 1C). For example, arecalculated version of RAM content may be transferred after a storagecontroller has determined that an operation has fully committed acrossthe storage system, or when fast-write memory on the device has reacheda certain used capacity, or after a certain amount of time, to ensureimprove safety of the data or to release addressable fast-write capacityfor reuse. This mechanism may be used, for example, to avoid a secondtransfer over a bus (e.g., 128 a, 128 b) from the storage controllers125 a, 125 b. In one embodiment, a recalculation may include compressingdata, attaching indexing or other metadata, combining multiple datasegments together, performing erasure code calculations, etc.

In one embodiment, under direction from a storage controller 125 a, 125b, a storage device controller 119 a, 119 b may be operable to calculateand transfer data to other storage devices from data stored in RAM(e.g., RAM 121 of FIG. 1C) without involvement of the storagecontrollers 125 a, 125 b. This operation may be used to mirror datastored in one controller 125 a to another controller 125 b, or it couldbe used to offload compression, data aggregation, and/or erasure codingcalculations and transfers to storage devices to reduce load on storagecontrollers or the storage controller interface 129 a, 129 b to the PCIbus 128 a, 128 b.

A storage device controller 119 may include mechanisms for implementinghigh availability primitives for use by other parts of a storage systemexternal to the Dual PCI storage device 118. For example, reservation orexclusion primitives may be provided so that, in a storage system withtwo storage controllers providing a highly available storage service,one storage controller may prevent the other storage controller fromaccessing or continuing to access the storage device. This could beused, for example, in cases where one controller detects that the othercontroller is not functioning properly or where the interconnect betweenthe two storage controllers may itself not be functioning properly.

In one embodiment, a storage system for use with Dual PCI direct mappedstorage devices with separately addressable fast write storage includessystems that manage erase blocks or groups of erase blocks as allocationunits for storing data on behalf of the storage service, or for storingmetadata (e.g., indexes, logs, etc.) associated with the storageservice, or for proper management of the storage system itself. Flashpages, which may be a few kilobytes in size, may be written as dataarrives or as the storage system is to persist data for long intervalsof time (e.g., above a defined threshold of time). To commit data morequickly, or to reduce the number of writes to the Flash memory devices,the storage controllers may first write data into the separatelyaddressable fast write storage on one more storage devices.

In one embodiment, the storage controllers 125 a, 125 b may initiate theuse of erase blocks within and across storage devices (e.g., 118) inaccordance with an age and expected remaining lifespan of the storagedevices, or based on other statistics. The storage controllers 125 a,125 b may initiate garbage collection and data migration data betweenstorage devices in accordance with pages that are no longer needed aswell as to manage Flash page and erase block lifespans and to manageoverall system performance.

In one embodiment, the storage system 124 may utilize mirroring and/orerasure coding schemes as part of storing data into addressable fastwrite storage and/or as part of writing data into allocation unitsassociated with erase blocks. Erasure codes may be used across storagedevices, as well as within erase blocks or allocation units, or withinand across Flash memory devices on a single storage device, to provideredundancy against single or multiple storage device failures or toprotect against internal corruptions of Flash memory pages resultingfrom Flash memory operations or from degradation of Flash memory cells.Mirroring and erasure coding at various levels may be used to recoverfrom multiple types of failures that occur separately or in combination.

The embodiments depicted with reference to FIGS. 2A-G illustrate astorage cluster that stores user data, such as user data originatingfrom one or more user or client systems or other sources external to thestorage cluster. The storage cluster distributes user data acrossstorage nodes housed within a chassis, or across multiple chassis, usingerasure coding and redundant copies of metadata. Erasure coding refersto a method of data protection or reconstruction in which data is storedacross a set of different locations, such as disks, storage nodes orgeographic locations. Flash memory is one type of solid-state memorythat may be integrated with the embodiments, although the embodimentsmay be extended to other types of solid-state memory or other storagemedium, including non-solid state memory. Control of storage locationsand workloads are distributed across the storage locations in aclustered peer-to-peer system. Tasks such as mediating communicationsbetween the various storage nodes, detecting when a storage node hasbecome unavailable, and balancing I/Os (inputs and outputs) across thevarious storage nodes, are all handled on a distributed basis. Data islaid out or distributed across multiple storage nodes in data fragmentsor stripes that support data recovery in some embodiments. Ownership ofdata can be reassigned within a cluster, independent of input and outputpatterns. This architecture described in more detail below allows astorage node in the cluster to fail, with the system remainingoperational, since the data can be reconstructed from other storagenodes and thus remain available for input and output operations. Invarious embodiments, a storage node may be referred to as a clusternode, a blade, or a server.

The storage cluster may be contained within a chassis, i.e., anenclosure housing one or more storage nodes. A mechanism to providepower to each storage node, such as a power distribution bus, and acommunication mechanism, such as a communication bus that enablescommunication between the storage nodes are included within the chassis.The storage cluster can run as an independent system in one locationaccording to some embodiments. In one embodiment, a chassis contains atleast two instances of both the power distribution and the communicationbus which may be enabled or disabled independently. The internalcommunication bus may be an Ethernet bus, however, other technologiessuch as Peripheral Component Interconnect (PCI) Express, InfiniBand, andothers, are equally suitable. The chassis provides a port for anexternal communication bus for enabling communication between multiplechassis, directly or through a switch, and with client systems. Theexternal communication may use a technology such as Ethernet,InfiniBand, Fibre Channel, etc. In some embodiments, the externalcommunication bus uses different communication bus technologies forinter-chassis and client communication. If a switch is deployed withinor between chassis, the switch may act as a translation between multipleprotocols or technologies. When multiple chassis are connected to definea storage cluster, the storage cluster may be accessed by a client usingeither proprietary interfaces or standard interfaces such as networkfile system (NFS), common internet file system (CIFS), small computersystem interface (SCSI) or hypertext transfer protocol (HTTP).Translation from the client protocol may occur at the switch, chassisexternal communication bus or within each storage node. In someembodiments, multiple chassis may be coupled or connected to each otherthrough an aggregator switch. A portion and/or all of the coupled orconnected chassis may be designated as a storage cluster. As discussedabove, each chassis can have multiple blades, each blade has a MAC(media access control) address, but the storage cluster is presented toan external network as having a single cluster IP (Internet Protocol)address and a single MAC address in some embodiments.

Each storage node may be one or more storage servers and each storageserver is connected to one or more non-volatile solid state memoryunits, which may be referred to as storage units or storage devices. Oneembodiment includes a single storage server in each storage node andbetween one to eight non-volatile solid state memory units, however thisone example is not meant to be limiting. The storage server may includea processor, dynamic random access memory (DRAM) and interfaces for theinternal communication bus and power distribution for each of the powerbuses. Inside the storage node, the interfaces and storage unit share acommunication bus, e.g., PCI Express, in some embodiments. Thenon-volatile solid state memory units may directly access the internalcommunication bus interface through a storage node communication bus, orrequest the storage node to access the bus interface. The non-volatilesolid state memory unit contains an embedded central processing unit(CPU), solid state storage controller, and a quantity of solid statemass storage, e.g., between 2-32 terabytes (TB) in some embodiments. Anembedded volatile storage medium, such as DRAM, and an energy reserveapparatus are included in the non-volatile solid state memory unit. Insome embodiments, the energy reserve apparatus is a capacitor,super-capacitor, or battery that enables transferring a subset of DRAMcontents to a stable storage medium in the case of power loss. In someembodiments, the non-volatile solid state memory unit is constructedwith a storage class memory, such as phase change or magnetoresistiverandom access memory (MRAM) that substitutes for DRAM and enables areduced power hold-up apparatus.

One of many features of the storage nodes and non-volatile solid statestorage is the ability to proactively rebuild data in a storage cluster.The storage nodes and non-volatile solid state storage can determinewhen a storage node or non-volatile solid state storage in the storagecluster is unreachable, independent of whether there is an attempt toread data involving that storage node or non-volatile solid statestorage. The storage nodes and non-volatile solid state storage thencooperate to recover and rebuild the data in at least partially newlocations. This constitutes a proactive rebuild, in that the systemrebuilds data without waiting until the data is needed for a read accessinitiated from a client system employing the storage cluster. These andfurther details of the storage memory and operation thereof arediscussed below.

FIG. 2A is a perspective view of a storage cluster 161, with multiplestorage nodes 150 and internal solid-state memory coupled to eachstorage node to provide network attached storage or storage areanetwork, in accordance with some embodiments. A network attachedstorage, storage area network, or a storage cluster, or other storagememory, could include one or more storage clusters 161, each having oneor more storage nodes 150, in a flexible and reconfigurable arrangementof both the physical components and the amount of storage memoryprovided thereby. The storage cluster 161 is designed to fit in a rack,and one or more racks can be set up and populated as desired for thestorage memory. The storage cluster 161 has a chassis 138 havingmultiple slots 142. It should be appreciated that chassis 138 may bereferred to as a housing, enclosure, or rack unit. In one embodiment,the chassis 138 has fourteen slots 142, although other numbers of slotsare readily devised. For example, some embodiments have four slots,eight slots, sixteen slots, thirty-two slots, or other suitable numberof slots. Each slot 142 can accommodate one storage node 150 in someembodiments. Chassis 138 includes flaps 148 that can be utilized tomount the chassis 138 on a rack. Fans 144 provide air circulation forcooling of the storage nodes 150 and components thereof, although othercooling components could be used, or an embodiment could be devisedwithout cooling components. A switch fabric 146 couples storage nodes150 within chassis 138 together and to a network for communication tothe memory. In an embodiment depicted in FIG. 1, the slots 142 to theleft of the switch fabric 146 and fans 144 are shown occupied by storagenodes 150, while the slots 142 to the right of the switch fabric 146 andfans 144 are empty and available for insertion of storage node 150 forillustrative purposes. This configuration is one example, and one ormore storage nodes 150 could occupy the slots 142 in various furtherarrangements. The storage node arrangements need not be sequential oradjacent in some embodiments. Storage nodes 150 are hot pluggable,meaning that a storage node 150 can be inserted into a slot 142 in thechassis 138, or removed from a slot 142, without stopping or poweringdown the system. Upon insertion or removal of storage node 150 from slot142, the system automatically reconfigures in order to recognize andadapt to the change. Reconfiguration, in some embodiments, includesrestoring redundancy and/or rebalancing data or load.

Each storage node 150 can have multiple components. In the embodimentshown here, the storage node 150 includes a printed circuit board 159populated by a CPU 156, i.e., processor, a memory 154 coupled to the CPU156, and a non-volatile solid state storage 152 coupled to the CPU 156,although other mountings and/or components could be used in furtherembodiments. The memory 154 has instructions which are executed by theCPU 156 and/or data operated on by the CPU 156. As further explainedbelow, the non-volatile solid state storage 152 includes flash or, infurther embodiments, other types of solid-state memory.

Referring to FIG. 2A, storage cluster 161 is scalable, meaning thatstorage capacity with non-uniform storage sizes is readily added, asdescribed above. One or more storage nodes 150 can be plugged into orremoved from each chassis and the storage cluster self-configures insome embodiments. Plug-in storage nodes 150, whether installed in achassis as delivered or later added, can have different sizes. Forexample, in one embodiment a storage node 150 can have any multiple of 4TB, e.g., 8 TB, 12 TB, 16 TB, 32 TB, etc. In further embodiments, astorage node 150 could have any multiple of other storage amounts orcapacities. Storage capacity of each storage node 150 is broadcast, andinfluences decisions of how to stripe the data. For maximum storageefficiency, an embodiment can self-configure as wide as possible in thestripe, subject to a predetermined requirement of continued operationwith loss of up to one, or up to two, non-volatile solid state storageunits 152 or storage nodes 150 within the chassis.

FIG. 2B is a block diagram showing a communications interconnect 171 andpower distribution bus 172 coupling multiple storage nodes 150.Referring back to FIG. 2A, the communications interconnect 171 can beincluded in or implemented with the switch fabric 146 in someembodiments. Where multiple storage clusters 161 occupy a rack, thecommunications interconnect 171 can be included in or implemented with atop of rack switch, in some embodiments. As illustrated in FIG. 2B,storage cluster 161 is enclosed within a single chassis 138. Externalport 176 is coupled to storage nodes 150 through communicationsinterconnect 171, while external port 174 is coupled directly to astorage node. External power port 178 is coupled to power distributionbus 172. Storage nodes 150 may include varying amounts and differingcapacities of non-volatile solid state storage 152 as described withreference to FIG. 2A. In addition, one or more storage nodes 150 may bea compute only storage node as illustrated in FIG. 2B. Authorities 168are implemented on the non-volatile solid state storages 152, forexample as lists or other data structures stored in memory. In someembodiments the authorities are stored within the non-volatile solidstate storage 152 and supported by software executing on a controller orother processor of the non-volatile solid state storage 152. In afurther embodiment, authorities 168 are implemented on the storage nodes150, for example as lists or other data structures stored in the memory154 and supported by software executing on the CPU 156 of the storagenode 150. Authorities 168 control how and where data is stored in thenon-volatile solid state storages 152 in some embodiments. This controlassists in determining which type of erasure coding scheme is applied tothe data, and which storage nodes 150 have which portions of the data.Each authority 168 may be assigned to a non-volatile solid state storage152. Each authority may control a range of inode numbers, segmentnumbers, or other data identifiers which are assigned to data by a filesystem, by the storage nodes 150, or by the non-volatile solid statestorage 152, in various embodiments.

Every piece of data, and every piece of metadata, has redundancy in thesystem in some embodiments. In addition, every piece of data and everypiece of metadata has an owner, which may be referred to as anauthority. If that authority is unreachable, for example through failureof a storage node, there is a plan of succession for how to find thatdata or that metadata. In various embodiments, there are redundantcopies of authorities 168. Authorities 168 have a relationship tostorage nodes 150 and non-volatile solid state storage 152 in someembodiments. Each authority 168, covering a range of data segmentnumbers or other identifiers of the data, may be assigned to a specificnon-volatile solid state storage 152. In some embodiments theauthorities 168 for all of such ranges are distributed over thenon-volatile solid state storages 152 of a storage cluster. Each storagenode 150 has a network port that provides access to the non-volatilesolid state storage(s) 152 of that storage node 150. Data can be storedin a segment, which is associated with a segment number and that segmentnumber is an indirection for a configuration of a RAID (redundant arrayof independent disks) stripe in some embodiments. The assignment and useof the authorities 168 thus establishes an indirection to data.Indirection may be referred to as the ability to reference dataindirectly, in this case via an authority 168, in accordance with someembodiments. A segment identifies a set of non-volatile solid statestorage 152 and a local identifier into the set of non-volatile solidstate storage 152 that may contain data. In some embodiments, the localidentifier is an offset into the device and may be reused sequentiallyby multiple segments. In other embodiments the local identifier isunique for a specific segment and never reused. The offsets in thenon-volatile solid state storage 152 are applied to locating data forwriting to or reading from the non-volatile solid state storage 152 (inthe form of a RAID stripe). Data is striped across multiple units ofnon-volatile solid state storage 152, which may include or be differentfrom the non-volatile solid state storage 152 having the authority 168for a particular data segment.

If there is a change in where a particular segment of data is located,e.g., during a data move or a data reconstruction, the authority 168 forthat data segment should be consulted, at that non-volatile solid statestorage 152 or storage node 150 having that authority 168. In order tolocate a particular piece of data, embodiments calculate a hash valuefor a data segment or apply an inode number or a data segment number.The output of this operation points to a non-volatile solid statestorage 152 having the authority 168 for that particular piece of data.In some embodiments there are two stages to this operation. The firststage maps an entity identifier (ID), e.g., a segment number, inodenumber, or directory number to an authority identifier. This mapping mayinclude a calculation such as a hash or a bit mask. The second stage ismapping the authority identifier to a particular non-volatile solidstate storage 152, which may be done through an explicit mapping. Theoperation is repeatable, so that when the calculation is performed, theresult of the calculation repeatably and reliably points to a particularnon-volatile solid state storage 152 having that authority 168. Theoperation may include the set of reachable storage nodes as input. Ifthe set of reachable non-volatile solid state storage units changes theoptimal set changes. In some embodiments, the persisted value is thecurrent assignment (which is always true) and the calculated value isthe target assignment the cluster will attempt to reconfigure towards.This calculation may be used to determine the optimal non-volatile solidstate storage 152 for an authority in the presence of a set ofnon-volatile solid state storage 152 that are reachable and constitutethe same cluster. The calculation also determines an ordered set of peernon-volatile solid state storage 152 that will also record the authorityto non-volatile solid state storage mapping so that the authority may bedetermined even if the assigned non-volatile solid state storage isunreachable. A duplicate or substitute authority 168 may be consulted ifa specific authority 168 is unavailable in some embodiments.

With reference to FIGS. 2A and 2B, two of the many tasks of the CPU 156on a storage node 150 are to break up write data, and reassemble readdata. When the system has determined that data is to be written, theauthority 168 for that data is located as above. When the segment ID fordata is already determined the request to write is forwarded to thenon-volatile solid state storage 152 currently determined to be the hostof the authority 168 determined from the segment. The host CPU 156 ofthe storage node 150, on which the non-volatile solid state storage 152and corresponding authority 168 reside, then breaks up or shards thedata and transmits the data out to various non-volatile solid statestorage 152. The transmitted data is written as a data stripe inaccordance with an erasure coding scheme. In some embodiments, data isrequested to be pulled, and in other embodiments, data is pushed. Inreverse, when data is read, the authority 168 for the segment IDcontaining the data is located as described above. The host CPU 156 ofthe storage node 150 on which the non-volatile solid state storage 152and corresponding authority 168 reside requests the data from thenon-volatile solid state storage and corresponding storage nodes pointedto by the authority. In some embodiments the data is read from flashstorage as a data stripe. The host CPU 156 of storage node 150 thenreassembles the read data, correcting any errors (if present) accordingto the appropriate erasure coding scheme, and forwards the reassembleddata to the network. In further embodiments, some or all of these taskscan be handled in the non-volatile solid state storage 152. In someembodiments, the segment host requests the data be sent to storage node150 by requesting pages from storage and then sending the data to thestorage node making the original request.

In some systems, for example in UNIX-style file systems, data is handledwith an index node or inode, which specifies a data structure thatrepresents an object in a file system. The object could be a file or adirectory, for example. Metadata may accompany the object, as attributessuch as permission data and a creation timestamp, among otherattributes. A segment number could be assigned to all or a portion ofsuch an object in a file system. In other systems, data segments arehandled with a segment number assigned elsewhere. For purposes ofdiscussion, the unit of distribution is an entity, and an entity can bea file, a directory or a segment. That is, entities are units of data ormetadata stored by a storage system. Entities are grouped into setscalled authorities. Each authority has an authority owner, which is astorage node that has the exclusive right to update the entities in theauthority. In other words, a storage node contains the authority, andthat the authority, in turn, contains entities.

A segment is a logical container of data in accordance with someembodiments. A segment is an address space between medium address spaceand physical flash locations, i.e., the data segment number, are in thisaddress space. Segments may also contain meta-data, which enable dataredundancy to be restored (rewritten to different flash locations ordevices) without the involvement of higher level software. In oneembodiment, an internal format of a segment contains client data andmedium mappings to determine the position of that data. Each datasegment is protected, e.g., from memory and other failures, by breakingthe segment into a number of data and parity shards, where applicable.The data and parity shards are distributed, i.e., striped, acrossnon-volatile solid state storage 152 coupled to the host CPUs 156 (SeeFIGS. 2E and 2G) in accordance with an erasure coding scheme. Usage ofthe term segments refers to the container and its place in the addressspace of segments in some embodiments. Usage of the term stripe refersto the same set of shards as a segment and includes how the shards aredistributed along with redundancy or parity information in accordancewith some embodiments.

A series of address-space transformations takes place across an entirestorage system. At the top are the directory entries (file names) whichlink to an inode. Modes point into medium address space, where data islogically stored. Medium addresses may be mapped through a series ofindirect mediums to spread the load of large files, or implement dataservices like deduplication or snapshots. Medium addresses may be mappedthrough a series of indirect mediums to spread the load of large files,or implement data services like deduplication or snapshots. Segmentaddresses are then translated into physical flash locations. Physicalflash locations have an address range bounded by the amount of flash inthe system in accordance with some embodiments. Medium addresses andsegment addresses are logical containers, and in some embodiments use a128 bit or larger identifier so as to be practically infinite, with alikelihood of reuse calculated as longer than the expected life of thesystem. Addresses from logical containers are allocated in ahierarchical fashion in some embodiments. Initially, each non-volatilesolid state storage unit 152 may be assigned a range of address space.Within this assigned range, the non-volatile solid state storage 152 isable to allocate addresses without synchronization with othernon-volatile solid state storage 152.

Data and metadata is stored by a set of underlying storage layouts thatare optimized for varying workload patterns and storage devices. Theselayouts incorporate multiple redundancy schemes, compression formats andindex algorithms. Some of these layouts store information aboutauthorities and authority masters, while others store file metadata andfile data. The redundancy schemes include error correction codes thattolerate corrupted bits within a single storage device (such as a NANDflash chip), erasure codes that tolerate the failure of multiple storagenodes, and replication schemes that tolerate data center or regionalfailures. In some embodiments, low density parity check (LDPC) code isused within a single storage unit. Reed-Solomon encoding is used withina storage cluster, and mirroring is used within a storage grid in someembodiments. Metadata may be stored using an ordered log structuredindex (such as a Log Structured Merge Tree), and large data may not bestored in a log structured layout.

In order to maintain consistency across multiple copies of an entity,the storage nodes agree implicitly on two things through calculations:(1) the authority that contains the entity, and (2) the storage nodethat contains the authority. The assignment of entities to authoritiescan be done by pseudo randomly assigning entities to authorities, bysplitting entities into ranges based upon an externally produced key, orby placing a single entity into each authority. Examples of pseudorandomschemes are linear hashing and the Replication Under Scalable Hashing(RUSH) family of hashes, including Controlled Replication Under ScalableHashing (CRUSH). In some embodiments, pseudo-random assignment isutilized only for assigning authorities to nodes because the set ofnodes can change. The set of authorities cannot change so any subjectivefunction may be applied in these embodiments. Some placement schemesautomatically place authorities on storage nodes, while other placementschemes rely on an explicit mapping of authorities to storage nodes. Insome embodiments, a pseudorandom scheme is utilized to map from eachauthority to a set of candidate authority owners. A pseudorandom datadistribution function related to CRUSH may assign authorities to storagenodes and create a list of where the authorities are assigned. Eachstorage node has a copy of the pseudorandom data distribution function,and can arrive at the same calculation for distributing, and laterfinding or locating an authority. Each of the pseudorandom schemesrequires the reachable set of storage nodes as input in some embodimentsin order to conclude the same target nodes. Once an entity has beenplaced in an authority, the entity may be stored on physical devices sothat no expected failure will lead to unexpected data loss. In someembodiments, rebalancing algorithms attempt to store the copies of allentities within an authority in the same layout and on the same set ofmachines.

Examples of expected failures include device failures, stolen machines,datacenter fires, and regional disasters, such as nuclear or geologicalevents. Different failures lead to different levels of acceptable dataloss. In some embodiments, a stolen storage node impacts neither thesecurity nor the reliability of the system, while depending on systemconfiguration, a regional event could lead to no loss of data, a fewseconds or minutes of lost updates, or even complete data loss.

In the embodiments, the placement of data for storage redundancy isindependent of the placement of authorities for data consistency. Insome embodiments, storage nodes that contain authorities do not containany persistent storage. Instead, the storage nodes are connected tonon-volatile solid state storage units that do not contain authorities.The communications interconnect between storage nodes and non-volatilesolid state storage units consists of multiple communicationtechnologies and has non-uniform performance and fault tolerancecharacteristics. In some embodiments, as mentioned above, non-volatilesolid state storage units are connected to storage nodes via PCIexpress, storage nodes are connected together within a single chassisusing Ethernet backplane, and chassis are connected together to form astorage cluster. Storage clusters are connected to clients usingEthernet or fiber channel in some embodiments. If multiple storageclusters are configured into a storage grid, the multiple storageclusters are connected using the Internet or other long-distancenetworking links, such as a “metro scale” link or private link that doesnot traverse the internet.

Authority owners have the exclusive right to modify entities, to migrateentities from one non-volatile solid state storage unit to anothernon-volatile solid state storage unit, and to add and remove copies ofentities. This allows for maintaining the redundancy of the underlyingdata. When an authority owner fails, is going to be decommissioned, oris overloaded, the authority is transferred to a new storage node.Transient failures make it non-trivial to ensure that all non-faultymachines agree upon the new authority location. The ambiguity thatarises due to transient failures can be achieved automatically by aconsensus protocol such as Paxos, hot-warm failover schemes, via manualintervention by a remote system administrator, or by a local hardwareadministrator (such as by physically removing the failed machine fromthe cluster, or pressing a button on the failed machine). In someembodiments, a consensus protocol is used, and failover is automatic. Iftoo many failures or replication events occur in too short a timeperiod, the system goes into a self-preservation mode and haltsreplication and data movement activities until an administratorintervenes in accordance with some embodiments.

As authorities are transferred between storage nodes and authorityowners update entities in their authorities, the system transfersmessages between the storage nodes and non-volatile solid state storageunits. With regard to persistent messages, messages that have differentpurposes are of different types. Depending on the type of the message,the system maintains different ordering and durability guarantees. Asthe persistent messages are being processed, the messages aretemporarily stored in multiple durable and non-durable storage hardwaretechnologies. In some embodiments, messages are stored in RAM, NVRAM andon NAND flash devices, and a variety of protocols are used in order tomake efficient use of each storage medium. Latency-sensitive clientrequests may be persisted in replicated NVRAM, and then later NAND,while background rebalancing operations are persisted directly to NAND.

Persistent messages are persistently stored prior to being transmitted.This allows the system to continue to serve client requests despitefailures and component replacement. Although many hardware componentscontain unique identifiers that are visible to system administrators,manufacturer, hardware supply chain and ongoing monitoring qualitycontrol infrastructure, applications running on top of theinfrastructure address virtualize addresses. These virtualized addressesdo not change over the lifetime of the storage system, regardless ofcomponent failures and replacements. This allows each component of thestorage system to be replaced over time without reconfiguration ordisruptions of client request processing, i.e., the system supportsnon-disruptive upgrades.

In some embodiments, the virtualized addresses are stored withsufficient redundancy. A continuous monitoring system correlateshardware and software status and the hardware identifiers. This allowsdetection and prediction of failures due to faulty components andmanufacturing details. The monitoring system also enables the proactivetransfer of authorities and entities away from impacted devices beforefailure occurs by removing the component from the critical path in someembodiments.

FIG. 2C is a multiple level block diagram, showing contents of a storagenode 150 and contents of a non-volatile solid state storage 152 of thestorage node 150. Data is communicated to and from the storage node 150by a network interface controller (NIC) 202 in some embodiments. Eachstorage node 150 has a CPU 156, and one or more non-volatile solid statestorage 152, as discussed above. Moving down one level in FIG. 2C, eachnon-volatile solid state storage 152 has a relatively fast non-volatilesolid state memory, such as nonvolatile random access memory (NVRAM)204, and flash memory 206. In some embodiments, NVRAM 204 may be acomponent that does not require program/erase cycles (DRAM, MRAM, PCM),and can be a memory that can support being written vastly more oftenthan the memory is read from. Moving down another level in FIG. 2C, theNVRAM 204 is implemented in one embodiment as high speed volatilememory, such as dynamic random access memory (DRAM) 216, backed up byenergy reserve 218. Energy reserve 218 provides sufficient electricalpower to keep the DRAM 216 powered long enough for contents to betransferred to the flash memory 206 in the event of power failure. Insome embodiments, energy reserve 218 is a capacitor, super-capacitor,battery, or other device, that supplies a suitable supply of energysufficient to enable the transfer of the contents of DRAM 216 to astable storage medium in the case of power loss. The flash memory 206 isimplemented as multiple flash dies 222, which may be referred to aspackages of flash dies 222 or an array of flash dies 222. It should beappreciated that the flash dies 222 could be packaged in any number ofways, with a single die per package, multiple dies per package (i.e.multichip packages), in hybrid packages, as bare dies on a printedcircuit board or other substrate, as encapsulated dies, etc. In theembodiment shown, the non-volatile solid state storage 152 has acontroller 212 or other processor, and an input output (I/O) port 210coupled to the controller 212. I/O port 210 is coupled to the CPU 156and/or the network interface controller 202 of the flash storage node150. Flash input output (I/O) port 220 is coupled to the flash dies 222,and a direct memory access unit (DMA) 214 is coupled to the controller212, the DRAM 216 and the flash dies 222. In the embodiment shown, theI/O port 210, controller 212, DMA unit 214 and flash I/O port 220 areimplemented on a programmable logic device (PLD) 208, e.g., a fieldprogrammable gate array (FPGA). In this embodiment, each flash die 222has pages, organized as sixteen kB (kilobyte) pages 224, and a register226 through which data can be written to or read from the flash die 222.In further embodiments, other types of solid-state memory are used inplace of, or in addition to flash memory illustrated within flash die222.

Storage clusters 161, in various embodiments as disclosed herein, can becontrasted with storage arrays in general. The storage nodes 150 arepart of a collection that creates the storage cluster 161. Each storagenode 150 owns a slice of data and computing required to provide thedata. Multiple storage nodes 150 cooperate to store and retrieve thedata. Storage memory or storage devices, as used in storage arrays ingeneral, are less involved with processing and manipulating the data.Storage memory or storage devices in a storage array receive commands toread, write, or erase data. The storage memory or storage devices in astorage array are not aware of a larger system in which they areembedded, or what the data means. Storage memory or storage devices instorage arrays can include various types of storage memory, such as RAM,solid state drives, hard disk drives, etc. The storage units 152described herein have multiple interfaces active simultaneously andserving multiple purposes. In some embodiments, some of thefunctionality of a storage node 150 is shifted into a storage unit 152,transforming the storage unit 152 into a combination of storage unit 152and storage node 150. Placing computing (relative to storage data) intothe storage unit 152 places this computing closer to the data itself.The various system embodiments have a hierarchy of storage node layerswith different capabilities. By contrast, in a storage array, acontroller owns and knows everything about all of the data that thecontroller manages in a shelf or storage devices. In a storage cluster161, as described herein, multiple controllers in multiple storage units152 and/or storage nodes 150 cooperate in various ways (e.g., forerasure coding, data sharding, metadata communication and redundancy,storage capacity expansion or contraction, data recovery, and so on).

FIG. 2D shows a storage server environment, which uses embodiments ofthe storage nodes 150 and storage units 152 of FIGS. 2A-C. In thisversion, each storage unit 152 has a processor such as controller 212(see FIG. 2C), an FPGA (field programmable gate array), flash memory206, and NVRAM 204 (which is super-capacitor backed DRAM 216, see FIGS.2B and 2C) on a PCIe (peripheral component interconnect express) boardin a chassis 138 (see FIG. 2A). The storage unit 152 may be implementedas a single board containing storage, and may be the largest tolerablefailure domain inside the chassis. In some embodiments, up to twostorage units 152 may fail and the device will continue with no dataloss.

The physical storage is divided into named regions based on applicationusage in some embodiments. The NVRAM 204 is a contiguous block ofreserved memory in the storage unit 152 DRAM 216, and is backed by NANDflash. NVRAM 204 is logically divided into multiple memory regionswritten for two as spool (e.g., spool_region). Space within the NVRAM204 spools is managed by each authority 168 independently. Each deviceprovides an amount of storage space to each authority 168. Thatauthority 168 further manages lifetimes and allocations within thatspace. Examples of a spool include distributed transactions or notions.When the primary power to a storage unit 152 fails, onboardsuper-capacitors provide a short duration of power hold up. During thisholdup interval, the contents of the NVRAM 204 are flushed to flashmemory 206. On the next power-on, the contents of the NVRAM 204 arerecovered from the flash memory 206.

As for the storage unit controller, the responsibility of the logical“controller” is distributed across each of the blades containingauthorities 168. This distribution of logical control is shown in FIG.2D as a host controller 242, mid-tier controller 244 and storage unitcontroller(s) 246. Management of the control plane and the storage planeare treated independently, although parts may be physically co-locatedon the same blade. Each authority 168 effectively serves as anindependent controller. Each authority 168 provides its own data andmetadata structures, its own background workers, and maintains its ownlifecycle.

FIG. 2E is a blade 252 hardware block diagram, showing a control plane254, compute and storage planes 256, 258, and authorities 168interacting with underlying physical resources, using embodiments of thestorage nodes 150 and storage units 152 of FIGS. 2A-C in the storageserver environment of FIG. 2D. The control plane 254 is partitioned intoa number of authorities 168 which can use the compute resources in thecompute plane 256 to run on any of the blades 252. The storage plane 258is partitioned into a set of devices, each of which provides access toflash 206 and NVRAM 204 resources.

In the compute and storage planes 256, 258 of FIG. 2E, the authorities168 interact with the underlying physical resources (i.e., devices).From the point of view of an authority 168, its resources are stripedover all of the physical devices. From the point of view of a device, itprovides resources to all authorities 168, irrespective of where theauthorities happen to run. Each authority 168 has allocated or has beenallocated one or more partitions 260 of storage memory in the storageunits 152, e.g. partitions 260 in flash memory 206 and NVRAM 204. Eachauthority 168 uses those allocated partitions 260 that belong to it, forwriting or reading user data. Authorities can be associated withdiffering amounts of physical storage of the system. For example, oneauthority 168 could have a larger number of partitions 260 or largersized partitions 260 in one or more storage units 152 than one or moreother authorities 168.

FIG. 2F depicts elasticity software layers in blades 252 of a storagecluster 161, in accordance with some embodiments. In the elasticitystructure, elasticity software is symmetric, i.e., each blade's computemodule 270 runs the three identical layers of processes depicted in FIG.2F. Storage managers 274 execute read and write requests from otherblades 252 for data and metadata stored in local storage unit 152 NVRAM204 and flash 206. Authorities 168 fulfill client requests by issuingthe necessary reads and writes to the blades 252 on whose storage units152 the corresponding data or metadata resides. Endpoints 272 parseclient connection requests received from switch fabric 146 supervisorysoftware, relay the client connection requests to the authorities 168responsible for fulfillment, and relay the authorities' 168 responses toclients. The symmetric three-layer structure enables the storagesystem's high degree of concurrency. Elasticity scales out efficientlyand reliably in these embodiments. In addition, elasticity implements aunique scale-out technique that balances work evenly across allresources regardless of client access pattern, and maximizes concurrencyby eliminating much of the need for inter-blade coordination thattypically occurs with conventional distributed locking.

Still referring to FIG. 2F, authorities 168 running in the computemodules 270 of a blade 252 perform the internal operations required tofulfill client requests. One feature of elasticity is that authorities168 are stateless, i.e., they cache active data and metadata in theirown blades' 168 DRAMs for fast access, but the authorities store everyupdate in their NVRAM 204 partitions on three separate blades 252 untilthe update has been written to flash 206. All the storage system writesto NVRAM 204 are in triplicate to partitions on three separate blades252 in some embodiments. With triple-mirrored NVRAM 204 and persistentstorage protected by parity and Reed-Solomon RAID checksums, the storagesystem can survive concurrent failure of two blades 252 with no loss ofdata, metadata, or access to either.

Because authorities 168 are stateless, they can migrate between blades252. Each authority 168 has a unique identifier. NVRAM 204 and flash 206partitions are associated with authorities' 168 identifiers, not withthe blades 252 on which they are running in some. Thus, when anauthority 168 migrates, the authority 168 continues to manage the samestorage partitions from its new location. When a new blade 252 isinstalled in an embodiment of the storage cluster 161, the systemautomatically rebalances load by:

Partitioning the new blade's 252 storage for use by the system'sauthorities 168,

Migrating selected authorities 168 to the new blade 252,

Starting endpoints 272 on the new blade 252 and including them in theswitch fabric's 146 client connection distribution algorithm.

From their new locations, migrated authorities 168 persist the contentsof their NVRAM 204 partitions on flash 206, process read and writerequests from other authorities 168, and fulfill the client requeststhat endpoints 272 direct to them. Similarly, if a blade 252 fails or isremoved, the system redistributes its authorities 168 among the system'sremaining blades 252. The redistributed authorities 168 continue toperform their original functions from their new locations.

FIG. 2G depicts authorities 168 and storage resources in blades 252 of astorage cluster, in accordance with some embodiments. Each authority 168is exclusively responsible for a partition of the flash 206 and NVRAM204 on each blade 252. The authority 168 manages the content andintegrity of its partitions independently of other authorities 168.Authorities 168 compress incoming data and preserve it temporarily intheir NVRAM 204 partitions, and then consolidate, RAID-protect, andpersist the data in segments of the storage in their flash 206partitions. As the authorities 168 write data to flash 206, storagemanagers 274 perform the necessary flash translation to optimize writeperformance and maximize media longevity. In the background, authorities168 “garbage collect,” or reclaim space occupied by data that clientshave made obsolete by overwriting the data. It should be appreciatedthat since authorities' 168 partitions are disjoint, there is no needfor distributed locking to execute client and writes or to performbackground functions.

The embodiments described herein may utilize various software,communication and/or networking protocols. In addition, theconfiguration of the hardware and/or software may be adjusted toaccommodate various protocols. For example, the embodiments may utilizeActive Directory, which is a database based system that providesauthentication, directory, policy, and other services in a WINDOWS™environment. In these embodiments, LDAP (Lightweight Directory AccessProtocol) is one example application protocol for querying and modifyingitems in directory service providers such as Active Directory. In someembodiments, a network lock manager (NLM) is utilized as a facility thatworks in cooperation with the Network File System (NFS) to provide aSystem V style of advisory file and record locking over a network. TheServer Message Block (SMB) protocol, one version of which is also knownas Common Internet File System (CIFS), may be integrated with thestorage systems discussed herein. SMP operates as an application-layernetwork protocol typically used for providing shared access to files,printers, and serial ports and miscellaneous communications betweennodes on a network. SMB also provides an authenticated inter-processcommunication mechanism. AMAZON™ S3 (Simple Storage Service) is a webservice offered by Amazon Web Services, and the systems described hereinmay interface with Amazon S3 through web services interfaces (REST(representational state transfer), SOAP (simple object access protocol),and BitTorrent). A RESTful API (application programming interface)breaks down a transaction to create a series of small modules. Eachmodule addresses a particular underlying part of the transaction. Thecontrol or permissions provided with these embodiments, especially forobject data, may include utilization of an access control list (ACL).The ACL is a list of permissions attached to an object and the ACLspecifies which users or system processes are granted access to objects,as well as what operations are allowed on given objects. The systems mayutilize Internet Protocol version 6 (IPv6), as well as IPv4, for thecommunications protocol that provides an identification and locationsystem for computers on networks and routes traffic across the Internet.The routing of packets between networked systems may include Equal-costmulti-path routing (ECMP), which is a routing strategy where next-hoppacket forwarding to a single destination can occur over multiple “bestpaths” which tie for top place in routing metric calculations.Multi-path routing can be used in conjunction with most routingprotocols, because it is a per-hop decision limited to a single router.The software may support Multi-tenancy, which is an architecture inwhich a single instance of a software application serves multiplecustomers. Each customer may be referred to as a tenant. Tenants may begiven the ability to customize some parts of the application, but maynot customize the application's code, in some embodiments. Theembodiments may maintain audit logs. An audit log is a document thatrecords an event in a computing system. In addition to documenting whatresources were accessed, audit log entries typically include destinationand source addresses, a timestamp, and user login information forcompliance with various regulations. The embodiments may support variouskey management policies, such as encryption key rotation. In addition,the system may support dynamic root passwords or some variationdynamically changing passwords.

FIG. 3A sets forth a diagram of a storage system 306 that is coupled fordata communications with a cloud services provider 302 in accordancewith some embodiments of the present disclosure. Although depicted inless detail, the storage system 306 depicted in FIG. 3A may be similarto the storage systems described above with reference to FIGS. 1A-1D andFIGS. 2A-2G. In some embodiments, the storage system 306 depicted inFIG. 3A may be embodied as a storage system that includes imbalancedactive/active controllers, as a storage system that includes balancedactive/active controllers, as a storage system that includesactive/active controllers where less than all of each controller'sresources are utilized such that each controller has reserve resourcesthat may be used to support failover, as a storage system that includesfully active/active controllers, as a storage system that includesdataset-segregated controllers, as a storage system that includesdual-layer architectures with front-end controllers and back-endintegrated storage controllers, as a storage system that includesscale-out clusters of dual-controller arrays, as well as combinations ofsuch embodiments.

In the example depicted in FIG. 3A, the storage system 306 is coupled tothe cloud services provider 302 via a data communications link 304. Thedata communications link 304 may be embodied as a dedicated datacommunications link, as a data communications pathway that is providedthrough the use of one or data communications networks such as a widearea network (WAN′) or local area network (‘LAN’), or as some othermechanism capable of transporting digital information between thestorage system 306 and the cloud services provider 302. Such a datacommunications link 304 may be fully wired, fully wireless, or someaggregation of wired and wireless data communications pathways. In suchan example, digital information may be exchanged between the storagesystem 306 and the cloud services provider 302 via the datacommunications link 304 using one or more data communications protocols.For example, digital information may be exchanged between the storagesystem 306 and the cloud services provider 302 via the datacommunications link 304 using the handheld device transfer protocol(‘HDTP’), hypertext transfer protocol (‘HTTP’), internet protocol(‘IP’), real-time transfer protocol (‘RTP’), transmission controlprotocol (‘TCP’), user datagram protocol (‘UDP’), wireless applicationprotocol (‘WAP’), or other protocol.

The cloud services provider 302 depicted in FIG. 3A may be embodied, forexample, as a system and computing environment that provides services tousers of the cloud services provider 302 through the sharing ofcomputing resources via the data communications link 304. The cloudservices provider 302 may provide on-demand access to a shared pool ofconfigurable computing resources such as computer networks, servers,storage, applications and services, and so on. The shared pool ofconfigurable resources may be rapidly provisioned and released to a userof the cloud services provider 302 with minimal management effort.Generally, the user of the cloud services provider 302 is unaware of theexact computing resources utilized by the cloud services provider 302 toprovide the services. Although in many cases such a cloud servicesprovider 302 may be accessible via the Internet, readers of skill in theart will recognize that any system that abstracts the use of sharedresources to provide services to a user through any data communicationslink may be considered a cloud services provider 302.

In the example depicted in FIG. 3A, the cloud services provider 302 maybe configured to provide a variety of services to the storage system 306and users of the storage system 306 through the implementation ofvarious service models. For example, the cloud services provider 302 maybe configured to provide services to the storage system 306 and users ofthe storage system 306 through the implementation of an infrastructureas a service (‘IaaS’) service model where the cloud services provider302 offers computing infrastructure such as virtual machines and otherresources as a service to subscribers. In addition, the cloud servicesprovider 302 may be configured to provide services to the storage system306 and users of the storage system 306 through the implementation of aplatform as a service (‘PaaS’) service model where the cloud servicesprovider 302 offers a development environment to application developers.Such a development environment may include, for example, an operatingsystem, programming-language execution environment, database, webserver, or other components that may be utilized by applicationdevelopers to develop and run software solutions on a cloud platform.Furthermore, the cloud services provider 302 may be configured toprovide services to the storage system 306 and users of the storagesystem 306 through the implementation of a software as a service(‘SaaS’) service model where the cloud services provider 302 offersapplication software, databases, as well as the platforms that are usedto run the applications to the storage system 306 and users of thestorage system 306, providing the storage system 306 and users of thestorage system 306 with on-demand software and eliminating the need toinstall and run the application on local computers, which may simplifymaintenance and support of the application. The cloud services provider302 may be further configured to provide services to the storage system306 and users of the storage system 306 through the implementation of anauthentication as a service (‘AaaS’) service model where the cloudservices provider 302 offers authentication services that can be used tosecure access to applications, data sources, or other resources. Thecloud services provider 302 may also be configured to provide servicesto the storage system 306 and users of the storage system 306 throughthe implementation of a storage as a service service model where thecloud services provider 302 offers access to its storage infrastructurefor use by the storage system 306 and users of the storage system 306.Readers will appreciate that the cloud services provider 302 may beconfigured to provide additional services to the storage system 306 andusers of the storage system 306 through the implementation of additionalservice models, as the service models described above are included onlyfor explanatory purposes and in no way represent a limitation of theservices that may be offered by the cloud services provider 302 or alimitation as to the service models that may be implemented by the cloudservices provider 302.

In the example depicted in FIG. 3A, the cloud services provider 302 maybe embodied, for example, as a private cloud, as a public cloud, or as acombination of a private cloud and public cloud. In an embodiment inwhich the cloud services provider 302 is embodied as a private cloud,the cloud services provider 302 may be dedicated to providing servicesto a single organization rather than providing services to multipleorganizations. In an embodiment where the cloud services provider 302 isembodied as a public cloud, the cloud services provider 302 may provideservices to multiple organizations. Public cloud and private clouddeployment models may differ and may come with various advantages anddisadvantages. For example, because a public cloud deployment involvesthe sharing of a computing infrastructure across different organization,such a deployment may not be ideal for organizations with securityconcerns, mission-critical workloads, uptime requirements demands, andso on. While a private cloud deployment can address some of theseissues, a private cloud deployment may require on-premises staff tomanage the private cloud. In still alternative embodiments, the cloudservices provider 302 may be embodied as a mix of a private and publiccloud services with a hybrid cloud deployment.

Although not explicitly depicted in FIG. 3A, readers will appreciatethat additional hardware components and additional software componentsmay be necessary to facilitate the delivery of cloud services to thestorage system 306 and users of the storage system 306. For example, thestorage system 306 may be coupled to (or even include) a cloud storagegateway. Such a cloud storage gateway may be embodied, for example, ashardware-based or software-based appliance that is located on premisewith the storage system 306. Such a cloud storage gateway may operate asa bridge between local applications that are executing on the storagearray 306 and remote, cloud-based storage that is utilized by thestorage array 306. Through the use of a cloud storage gateway,organizations may move primary iSCSI or NAS to the cloud servicesprovider 302, thereby enabling the organization to save space on theiron-premises storage systems. Such a cloud storage gateway may beconfigured to emulate a disk array, a block-based device, a file server,or other storage system that can translate the SCSI commands, fileserver commands, or other appropriate command into REST-space protocolsthat facilitate communications with the cloud services provider 302.

In order to enable the storage system 306 and users of the storagesystem 306 to make use of the services provided by the cloud servicesprovider 302, a cloud migration process may take place during whichdata, applications, or other elements from an organization's localsystems (or even from another cloud environment) are moved to the cloudservices provider 302. In order to successfully migrate data,applications, or other elements to the cloud services provider's 302environment, middleware such as a cloud migration tool may be utilizedto bridge gaps between the cloud services provider's 302 environment andan organization's environment. Such cloud migration tools may also beconfigured to address potentially high network costs and long transfertimes associated with migrating large volumes of data to the cloudservices provider 302, as well as addressing security concernsassociated with sensitive data to the cloud services provider 302 overdata communications networks. In order to further enable the storagesystem 306 and users of the storage system 306 to make use of theservices provided by the cloud services provider 302, a cloudorchestrator may also be used to arrange and coordinate automated tasksin pursuit of creating a consolidated process or workflow. Such a cloudorchestrator may perform tasks such as configuring various components,whether those components are cloud components or on-premises components,as well as managing the interconnections between such components. Thecloud orchestrator can simplify the inter-component communication andconnections to ensure that links are correctly configured andmaintained.

In the example depicted in FIG. 3A, and as described briefly above, thecloud services provider 302 may be configured to provide services to thestorage system 306 and users of the storage system 306 through the usageof a SaaS service model where the cloud services provider 302 offersapplication software, databases, as well as the platforms that are usedto run the applications to the storage system 306 and users of thestorage system 306, providing the storage system 306 and users of thestorage system 306 with on-demand software and eliminating the need toinstall and run the application on local computers, which may simplifymaintenance and support of the application. Such applications may takemany forms in accordance with various embodiments of the presentdisclosure. For example, the cloud services provider 302 may beconfigured to provide access to data analytics applications to thestorage system 306 and users of the storage system 306. Such dataanalytics applications may be configured, for example, to receivetelemetry data phoned home by the storage system 306. Such telemetrydata may describe various operating characteristics of the storagesystem 306 and may be analyzed, for example, to determine the health ofthe storage system 306, to identify workloads that are executing on thestorage system 306, to predict when the storage system 306 will run outof various resources, to recommend configuration changes, hardware orsoftware upgrades, workflow migrations, or other actions that mayimprove the operation of the storage system 306.

The cloud services provider 302 may also be configured to provide accessto virtualized computing environments to the storage system 306 andusers of the storage system 306. Such virtualized computing environmentsmay be embodied, for example, as a virtual machine or other virtualizedcomputer hardware platforms, virtual storage devices, virtualizedcomputer network resources, and so on. Examples of such virtualizedenvironments can include virtual machines that are created to emulate anactual computer, virtualized desktop environments that separate alogical desktop from a physical machine, virtualized file systems thatallow uniform access to different types of concrete file systems, andmany others.

For further explanation, FIG. 3B sets forth a diagram of a storagesystem 306 in accordance with some embodiments of the presentdisclosure. Although depicted in less detail, the storage system 306depicted in FIG. 3B may be similar to the storage systems describedabove with reference to FIGS. 1A-1D and FIGS. 2A-2G as the storagesystem may include many of the components described above.

The storage system 306 depicted in FIG. 3B may include storage resources308, which may be embodied in many forms. For example, in someembodiments the storage resources 308 can include nano-RAM or anotherform of nonvolatile random access memory that utilizes carbon nanotubesdeposited on a substrate. In some embodiments, the storage resources 308may include 3D crosspoint non-volatile memory in which bit storage isbased on a change of bulk resistance, in conjunction with a stackablecross-gridded data access array. In some embodiments, the storageresources 308 may include flash memory, including single-level cell(‘SLC’) NAND flash, multi-level cell (‘MLC’) NAND flash, triple-levelcell (TLC′) NAND flash, quad-level cell (‘QLC’) NAND flash, and others.In some embodiments, the storage resources 308 may include non-volatilemagnetoresistive random-access memory (‘MRAM’), including spin transfertorque (‘STT’) MRAM, in which data is stored through the use of magneticstorage elements. In some embodiments, the example storage resources 308may include non-volatile phase-change memory (‘PCM’) that may have theability to hold multiple bits in a single cell as cells can achieve anumber of distinct intermediary states. In some embodiments, the storageresources 308 may include quantum memory that allows for the storage andretrieval of photonic quantum information. In some embodiments, theexample storage resources 308 may include resistive random-access memory(‘ReRAM’) in which data is stored by changing the resistance across adielectric solid-state material. In some embodiments, the storageresources 308 may include storage class memory (‘SCM’) in whichsolid-state nonvolatile memory may be manufactured at a high densityusing some combination of sub-lithographic patterning techniques,multiple bits per cell, multiple layers of devices, and so on. Readerswill appreciate that other forms of computer memories and storagedevices may be utilized by the storage systems described above,including DRAM, SRAM, EEPROM, universal memory, and many others. Thestorage resources 308 depicted in FIG. 3A may be embodied in a varietyof form factors, including but not limited to, dual in-line memorymodules (‘DIMMs’), non-volatile dual in-line memory modules (‘NVDIMMs’),M.2, U.2, and others.

The example storage system 306 depicted in FIG. 3B may implement avariety of storage architectures. For example, storage systems inaccordance with some embodiments of the present disclosure may utilizeblock storage where data is stored in blocks, and each block essentiallyacts as an individual hard drive. Storage systems in accordance withsome embodiments of the present disclosure may utilize object storage,where data is managed as objects. Each object may include the dataitself, a variable amount of metadata, and a globally unique identifier,where object storage can be implemented at multiple levels (e.g., devicelevel, system level, interface level). Storage systems in accordancewith some embodiments of the present disclosure utilize file storage inwhich data is stored in a hierarchical structure. Such data may be savedin files and folders, and presented to both the system storing it andthe system retrieving it in the same format.

The example storage system 306 depicted in FIG. 3B may be embodied as astorage system in which additional storage resources can be addedthrough the use of a scale-up model, additional storage resources can beadded through the use of a scale-out model, or through some combinationthereof. In a scale-up model, additional storage may be added by addingadditional storage devices. In a scale-out model, however, additionalstorage nodes may be added to a cluster of storage nodes, where suchstorage nodes can include additional processing resources, additionalnetworking resources, and so on.

The storage system 306 depicted in FIG. 3B also includes communicationsresources 310 that may be useful in facilitating data communicationsbetween components within the storage system 306, as well as datacommunications between the storage system 306 and computing devices thatare outside of the storage system 306. The communications resources 310may be configured to utilize a variety of different protocols and datacommunication fabrics to facilitate data communications betweencomponents within the storage systems as well as computing devices thatare outside of the storage system. For example, the communicationsresources 310 can include fibre channel (‘FC’) technologies such as FCfabrics and FC protocols that can transport SCSI commands over FCnetworks. The communications resources 310 can also include FC overethernet (‘FCoE’) technologies through which FC frames are encapsulatedand transmitted over Ethernet networks. The communications resources 310can also include InfiniBand (‘IB’) technologies in which a switchedfabric topology is utilized to facilitate transmissions between channeladapters. The communications resources 310 can also include NVM Express(‘NVMe’) technologies and NVMe over fabrics (‘NVMeoF’) technologiesthrough which non-volatile storage media attached via a PCI express(‘PCIe’) bus may be accessed. The communications resources 310 can alsoinclude mechanisms for accessing storage resources 308 within thestorage system 306 utilizing serial attached SCSI (‘SAS’), serial ATA(‘SATA’) bus interfaces for connecting storage resources 308 within thestorage system 306 to host bus adapters within the storage system 306,internet small computer systems interface (iSCSI′) technologies toprovide block-level access to storage resources 308 within the storagesystem 306, and other communications resources that that may be usefulin facilitating data communications between components within thestorage system 306, as well as data communications between the storagesystem 306 and computing devices that are outside of the storage system306.

The storage system 306 depicted in FIG. 3B also includes processingresources 312 that may be useful in useful in executing computer programinstructions and performing other computational tasks within the storagesystem 306. The processing resources 312 may include one or moreapplication-specific integrated circuits (‘ASICs’) that are customizedfor some particular purpose as well as one or more central processingunits (‘CPUs’). The processing resources 312 may also include one ormore digital signal processors (‘DSPs’), one or more field-programmablegate arrays (‘FPGAs’), one or more systems on a chip (‘SoCs’), or otherform of processing resources 312. The storage system 306 may utilize thestorage resources 312 to perform a variety of tasks including, but notlimited to, supporting the execution of software resources 314 that willbe described in greater detail below.

The storage system 306 depicted in FIG. 3B also includes softwareresources 314 that, when executed by processing resources 312 within thestorage system 306, may perform various tasks. The software resources314 may include, for example, one or more modules of computer programinstructions that when executed by processing resources 312 within thestorage system 306 are useful in carrying out various data protectiontechniques to preserve the integrity of data that is stored within thestorage systems. Readers will appreciate that such data protectiontechniques may be carried out, for example, by system software executingon computer hardware within the storage system, by a cloud servicesprovider, or in other ways. Such data protection techniques can include,for example, data archiving techniques that cause data that is no longeractively used to be moved to a separate storage device or separatestorage system for long-term retention, data backup techniques throughwhich data stored in the storage system may be copied and stored in adistinct location to avoid data loss in the event of equipment failureor some other form of catastrophe with the storage system, datareplication techniques through which data stored in the storage systemis replicated to another storage system such that the data may beaccessible via multiple storage systems, data snapshotting techniquesthrough which the state of data within the storage system is captured atvarious points in time, data and database cloning techniques throughwhich duplicate copies of data and databases may be created, and otherdata protection techniques. Through the use of such data protectiontechniques, business continuity and disaster recovery objectives may bemet as a failure of the storage system may not result in the loss ofdata stored in the storage system.

The software resources 314 may also include software that is useful inimplementing software-defined storage (‘SDS’). In such an example, thesoftware resources 314 may include one or more modules of computerprogram instructions that, when executed, are useful in policy-basedprovisioning and management of data storage that is independent of theunderlying hardware. Such software resources 314 may be useful inimplementing storage virtualization to separate the storage hardwarefrom the software that manages the storage hardware.

The software resources 314 may also include software that is useful infacilitating and optimizing I/O operations that are directed to thestorage resources 308 in the storage system 306. For example, thesoftware resources 314 may include software modules that perform carryout various data reduction techniques such as, for example, datacompression, data deduplication, and others. The software resources 314may include software modules that intelligently group together I/Ooperations to facilitate better usage of the underlying storage resource308, software modules that perform data migration operations to migratefrom within a storage system, as well as software modules that performother functions. Such software resources 314 may be embodied as one ormore software containers or in many other ways.

Readers will appreciate that the various components depicted in FIG. 3Bmay be grouped into one or more optimized computing packages asconverged infrastructures. Such converged infrastructures may includepools of computers, storage and networking resources that can be sharedby multiple applications and managed in a collective manner usingpolicy-driven processes. Such converged infrastructures may minimizecompatibility issues between various components within the storagesystem 306 while also reducing various costs associated with theestablishment and operation of the storage system 306. Such convergedinfrastructures may be implemented with a converged infrastructurereference architecture, with standalone appliances, with a softwaredriven hyper-converged approach, or in other ways.

Readers will appreciate that the storage system 306 depicted in FIG. 3Bmay be useful for supporting various types of software applications. Forexample, the storage system 306 may be useful in supporting artificialintelligence applications, database applications, DevOps projects,electronic design automation tools, event-driven software applications,high performance computing applications, simulation applications,high-speed data capture and analysis applications, machine learningapplications, media production applications, media serving applications,picture archiving and communication systems (‘PACS’) applications,software development applications, and many other types of applicationsby providing storage resources to such applications.

With reference to FIGS. 2A-3B, in various embodiments of the storagecluster 160, load-balancing across the storage nodes 150 or blades 252is a stateless process in which each communication is treated asindependent of any other communication, for load-balancing purposes. TCP(transmission control protocol) is a stateful protocol, which allowsestablishment of a two-way connection between two endpoints (e.g.,computers or in the case of the storage cluster, a client and one of theblades 252, or more specifically, one of the storage nodes 150), forcommunication using packets between the endpoints on the TCP connection.Sometimes a blade 252 (or storage node 150) gets added to or removedfrom the storage cluster 160 and it is desired to shift load-balancingto include the new blade 252 or storage node 150, or operate properlywithout the removed blade 252 or storage node 150. However, the TCPconnection may not be correct for the revised membership of storagenodes 150 in the storage cluster 160, and load-balancing may be uneven.This can result in a stale TCP connection lingering on some of thestorage nodes 150 in the storage cluster 160, which can continue to useor consume resources.

If for any reason, there is another shift in load balancing and the TCPconnection moves back to the original blade 252, the stale connectioncan just stall I/O's, since both sides will have different activewindows. When there is a change in load balancing, a new storage node150 might start receiving packets from a client which do not belong toany valid connection. The new storage node 150 responds by resetting theTCP connection.

The embodiments employ a mechanism for resetting a TCP connection, whichsends a TCP reset packet (e.g., with the reset bit set in the TCPheader). This mechanism is applied to resetting TCP connections of theblades 252 (or storage nodes 150) and clients. Optionally, in someembodiments, the TCP resets are sent as out of band data or an out ofband communication (i.e., out of band control packets) specified asurgent, by setting the urgent bit in the header of each such packet. Ifa new blade 252 (or storage node 150) receives a packet that the newblade 252 does not understand, the new blade 252 sends out a packet witha message interpreted as “I don't understand” and this triggers thesending of the TCP reset packet by the host (e.g., one of the blades252, or the switch fabric). The TCP reset packet triggers the kernel inthe blade 252 or storage node 150 to “clean up” the connection at theother end. It should be appreciated that in order to avoid a staleconnection on the blade 252 or storage node 150 that originally hostedthe TCP connection, that blade 252 or storage node 150 needs to clean upthe TCP connection.

The load balancer/switching element in the storage cluster can detect aTCP reset originating from any storage node 150 and takes theresponsibility of conveying the requirement to clean up the TCPconnection to all the storage nodes 150 that are managed by the loadbalancer in some embodiments. There is traffic monitoring logic withineach blade 252 or storage node 150 that can detect packets from theconnection in some embodiments. The traffic monitoring logic detects aTCP reset packet, indicating that the blade 252 or storage node 150needs to clean up or reset the TCP connection information, and an agentinjects a locally and properly formatted TCP reset back to the storagenode 150 after determining the correct sequence numbers. This logiccleans up the TCP connection on the storage node 150 gracefully. A blade252 or storage node 150 that receives the TCP reset packet has theoption of reestablishing the TCP connection, which, for the client, maybe with a new or different blade 252, e.g., when adding a blade 252 tothe storage system. Thus, this stateless mechanism allows for loadbalancing more efficiently than load balancing when software isinvolved, i.e., for a stateful load balancer. Further details ofstateless load-balancing and the TCP reset mechanism are describedbelow.

FIG. 4 is a block diagram of a stateless load balancer 402 forembodiments of a storage cluster 160 such as shown in FIGS. 2A-3B.Features in the load balancer 402 can be implemented in hardware,firmware, software executing on a processor, data structure(s) inmemory, etc., in various combinations in various embodiments. There is atable 418 in the load balancer 402, for information about paths tostorage nodes (i.e., storage node path information), but no stateinformation about TCP connections. A switch control 414, which couldinclude one or more processors or controllers, e.g., a switchcontroller, maintains the table 418 with paths to the storage nodes, andoperates the switches 420 to load balance network communication packetsto the storage nodes 150 of the storage cluster 160. Storage nodes 150(not shown in FIG. 4, but see FIGS. 2A-2C and FIGS. 5-8, and FIGS. 2E-2Gdepicting blades 252 that can implement and include storage nodes 150)are free to establish TCP connections (e.g., with a client) and maintainTCP connection information. The load balancer 402, being stateless, isnot required to maintain TCP connection information. Adding more storagenodes, with each storage node tracking its own TCP connectioninformation, does not excessively burden any single component, andscales efficiently. In contrast, requiring a load balancer to bestateful and maintain TCP connection information for all storage nodescommunicating through the load balancer would not scale well with theaddition of more storage nodes.

Still referring to FIG. 4, to load balance packets across storage nodes150 of the storage cluster 160, each time a packet 408 arrives at theload balancer 402, the switch control 414 extracts the header 404 fromthe packet 408, or in some embodiments extracts a portion of the payload406 or a portion of the header 404 and a portion of the payload 406, anduses this extracted information from the packet 408 as an input to ahash function 410. Output from the hash function 410 is input to anindex generator 412, which points to the table 418 with the paths to thestorage nodes 150. Using the index from the index generator 412, whichis based on the hash function value generated from the header 404 and/orthe payload 406 of the packet 408, the switch control 414 selects a pathfrom the table 418. The load balancer 402 sends the packet 408 to thestorage node 150 on the selected path from the table 418, e.g., byhaving the switch control 414 operate the switches 420. As a result ofthe pseudorandom nature of hash function 410 output, the load balancer402 distributes packets in a pseudorandom manner.

It should be appreciated that in order to avoid sending a packet to astorage node that does not exist, or is unresponsive, and to assure thatall storage nodes receive some of the load balanced packets, the loadbalancer 402 maintains the table 418, and updates the table 418 for anyadded or removed storage nodes 150. Whenever a storage node 150 isremoved from the storage cluster 160, e.g., by physically removing ablade 252 from a chassis 138, a collective decision by storage nodes150, a user request, a failure of a storage node 150, etc., the switchcontrol 414 removes the associated paths from the table 418. Whenever astorage node 150 is added to the storage cluster 160, e.g., byphysically adding a blade 252 to the chassis 138, a collective decisionby storage nodes 150 to allocate a spare or idle storage node 150 orblade 252, a user request, etc., the switch control 414 adds anappropriate path to the table 418. Relatedly, if a storage node 150 orblade 252 is moved in the chassis 138, the switch control 414 makes theappropriate update to the paths listed in the table 418.

Because each change in membership of storage nodes 150 to the storagecluster 160 results in a change to the table 418 of FIG. 4, of paths tothe storage nodes 150, each such change affects the load-balancing. Apositive effect is that the load-balancing is always kept pseudorandomacross all of the active and accounted-for storage nodes 150 in thestorage cluster. Another effect is that the load-balancing can sendpackets associated with a specific TCP connection and a storage node 150to another storage node 150 that is not associated with that TCPconnection, as a result of an update to the table 418, which in turn isa result of a change in membership of storage nodes 150 to the storagecluster 160. To counter the latter effect, the embodiment of the loadbalancer 402 in FIG. 4 has a TCP reset module 416, with a trap 422. TheTCP reset module 416 monitors packets through the load balancer 402.When a packet 408 has a TCP reset, e.g., with the TCP reset bit set inthe header 404 of the packet 408, the trap 422 recognizes the TCP reset,and triggers the sending of further TCP reset packets as described belowwith reference to FIG. 6 and FIG. 8.

FIG. 5 illustrates a TCP connection 506 established between a client 504and a storage node 150 of a storage cluster 160, and a problem occurringwhen a stateless load balancer 402 sends a packet 502 associated withthe TCP connection 506 to another storage node 150. Before a storagenode was added or removed from the storage cluster 160, the loadbalancer 402 would consistently send packets 408 with the same header404 to the same storage node 150, since the hash function 410 resultsand index generated by the index generator 412 would be consistent andresult in consistent selection of paths from the table 418 (see FIG. 4).Thus, even though the load balancer 402 is stateless, a TCP connection506 is reliably serviced and preserved through the load balancer 402when there are no changes to membership of storage nodes 150 to thestorage cluster 160. However, once a storage node 150 is added to orremoved from the storage cluster 160, and the table 418 in the loadbalancer 402 changes, a packet 502 from the client 504, belonging to theTCP connection 506 established with one of the storage nodes 150 (e.g.,“storage node 2”) is delivered to another storage node 150 (e.g.,“storage node N”). This may be problematic both because the originalstorage node 150 with the TCP connection 506 does not receive the packet502 associated with the TCP connection 506, and the client 504 does notknow that the packet 502 did not get to the correct destinationaccording to the TCP connection 506. In addition, the storage node 150that receives the packet 502 but which is not part of the TCP connection506, may not know what to do with the packet 502.

FIG. 6 illustrates the storage node 150 sending out a TCP reset packet602, in a solution to the problem depicted in FIG. 5. The storage node150 that received the packet 502 associated with or belonging to the TCPconnection 506 of another storage node 150 sends a TCP reset packet 602to the client 504. Upon receiving the TCP reset packet 602, the client504 resets all TCP connection information, and may or may not seekanother TCP connection 506, at the option of the client 504. Upon havingthe TCP reset packet 602 travel through the load balancer 402 on the wayto the client 504, the load balancer 402 traps the TCP reset packet 602using the trap 422. The trap 422 recognizes the TCP reset packet 602,and triggers the switch control 414 to send more TCP reset packets 604to the storage nodes 150, for example to all of the storage nodes 150except the storage node 150 that sent the original TCP reset packet 602.Each storage node 150 that receives a TCP reset packet 604 resets TCPconnection information 708 (see FIG. 7). One of the storage nodes 150that receives such a TCP reset packet 604 will, by necessity, be thestorage node 150 that had the original TCP connection 506, as shown inFIG. 5, and will reset that TCP connection 506. Thus, after the storagenodes 150 have reset TCP connection information, and the client 504 hasreset TCP connection information, the storage system (i.e., storagecluster 160) and client 504 are in agreement that there is no more TCPconnection 506 between client 504 and the storage node 150 that had theoriginal TCP connection 506. Thus, the overall system has a consistentsystem state regarding TCP connections.

FIG. 7 depicts internal processes in a storage node 150 receiving a TCPreset packet 604. Each storage node 150 has a kernel 704 that maintainsTCP connection information 708 in memory, for any TCP connections 506.An agent 706 in the storage node 150, e.g., implemented in softwareexecuting on one or more processors 702 of the storage node 150,hardware, firmware or any combination thereof, performs packetmonitoring. In various embodiments, the agent 706 is not the same as anauthority 168, but is a standalone agent in the storage node 150. In afurther embodiment, the agent 706 could be one of the authorities 168with these added duties. The agent 706 understands the TCP window, fromthe packet monitoring. Upon recognition of a TCP reset packet 604, theagent 706 injects an appropriately formatted packet 710 (i.e., thepacket is a TCP reset formatted according to the TCP window) into thekernel 704. The packet 710 triggers the kernel 704 to reset or clean upthe TCP connection information 708.

FIG. 8 illustrates the storage node sending out a TCP reset packet 602,in a multi-chassis storage cluster 160 solution to the problem depictedin FIG. 5. Here, the storage nodes 150 of the storage cluster 160 occupymultiple chassis 138. Each chassis 138 has a load balancer 402 that loadbalances across the storage nodes 150 of that chassis 138. There is alsoa load balancer 402 that load balances across the multiple chassis 138of the storage system, for example a load balancer 402 implemented as atop of rack switch, or implemented in a network attached to the multiplechassis 138. These multiple levels of load-balancing can be viewed as adistributed load balancer. It is also possible, in a further embodiment,that the multiple levels of load-balancing could be integrated into asingle load balancer 402.

In additional related scenarios, one of the storage nodes 150 in one ofthe chassis 138 has the TCP connection 506 established, and storage nodemembership 150 changes in one or more of the chassis 138. Alternatively,one or more chassis 138 are added to or removed from the storage cluster160. Any of these could result in changes to the tables 418 in the loadbalancers 402 at one or more levels of load-balancing, as specific to agiven scenario. In any of these scenarios, the load-balancing could senda packet belonging to or associated with a TCP connection 506 from aclient 404 to a storage node 150 that is not associated with the TCPconnection 506, similar to the scenario of FIG. 5.

The storage node 150 that receives such a packet, but does not recognizethe packet since the storage node 150 is not associated with the TCPconnection 506, sends a TCP reset packet to the client 404. A trap inthe load balancer 402 that load balances across the multiple chassis 138traps the TCP reset packet 602, and sends out more TCP reset packets802, to the load balancers 402 in the multiple chassis 138, in responseto trapping the TCP reset packet 602. Each load balancer 402 in achassis 138 traps the additional reset packet 802, and sends out stillmore TCP reset packets 804 to the storage nodes 150 in that chassis 138,in response to trapping the TCP reset packet 802. In a variation, theload balancer 402 in the chassis 138 where the TCP reset packet 602originated from a storage node 150 behaves as does the load balancer 402in the embodiment shown in FIG. 6, trapping the TCP reset packet 602 andsending TCP reset packets 604 to storage nodes 150 in that chassis 138,except for the storage node 150 that originated the TCP reset packet602. In such a variation, the load balancer 402 that load balancesacross the multiple chassis 138 sends the additional TCP reset packets802 only to those chassis 138 that did not originate the TCP resetpacket 602. Thus, in all of these variations, the client 404 and allstorage nodes 150 receive a TCP reset packet 804, except the storagenode 150 that originated the TCP reset packet 602. Once the storagenodes 150 and client 404 reset the TCP connection information 708, theclient 404 and storage nodes 150 are in agreement that there is no TCPconnection 506. In a variation, load balancers 402 send TCP resets toall chassis 138 and all storage nodes 150, and whichever storage node150 originated the TCP reset 602 receives a redundant TCP reset but doesnot need to act upon the TCP reset since that storage node 150 did nothave the TCP connection 506 to begin with. Or, that storage node 150proceeds and resets TCP connection information. A similar variationapplies to the load balancer 402 in a single chassis storage system, asshown in FIG. 5.

FIG. 9 is a flow diagram of a method of resetting a stateful connectionin a storage cluster with stateless load-balancing, which can bepracticed by embodiments of storage clusters as described herein, andfurther storage clusters and storage systems. The method can bepracticed by one or more processors in such storage systems. In anaction 902, a stateful connection is established between a client and afirst storage node, in a storage cluster. The stateful connection is aTCP connection between client and storage node, in various embodiments.In an action 904, the storage node membership in the storage cluster ischanged. This could occur by addition, removal or failure of one or morestorage nodes or one or more chassis with storage nodes. In an action906, responsive to the change to storage node membership in the storagecluster, a storage node path table is updated in a stateless loadbalancer. In some scenarios, multiple levels of load-balancing arepresent, and each level could have a storage node path table, with oneor more such levels updated. In an action 908, packets are load balancedaccording to the storage node path table(s).

In an action 910, a packet associated with the stateful connection ofthe first storage node is received at a second storage node in thestorage cluster. The erroneous or problematic delivery of the packet isa result of the changed storage node path table in the stateless loadbalancer(s), which in turn is a result of the change to storage nodemembership in the storage cluster. In an action 912, a TCP reset packetis sent from the second storage node to the client, responsive toreceiving the packet associated with the stateful connection of thefirst storage node. The second storage node could obtain the addressinginformation for the client from the erroneously received packet. In anaction 914, the TCP reset packet is trapped at the stateless loadbalancer. In an action 916, the stateless load balancer sends furtherTCP reset packets to storage nodes. In some embodiments, these furtherTCP reset packets are sent to all storage nodes in the storage clusterexcept the second storage node. Actions 914 and 916 are applicable tosingle chassis storage clusters and multi-chassis storage clusters. Inan action 918, the stateful connection information is reset in thestorage nodes, responsive to receiving the TCP reset packets. With theclient also receiving the original TCP reset packet, the client and allstorage nodes become in agreement that there is no more TCP connectionbetween the client and the storage node(s).

It should be appreciated that the methods described herein may beperformed with a digital processing system, such as a conventional,general-purpose computer system. Special purpose computers, which aredesigned or programmed to perform only one function may be used in thealternative. FIG. 10 is an illustration showing an exemplary computingdevice which may implement the embodiments described herein. Thecomputing device of FIG. 10 may be used to perform embodiments of thefunctionality for the TCP reset mechanism(s) in accordance with someembodiments. The computing device includes a central processing unit(CPU) 1001, which is coupled through a bus 1005 to a memory 1003, andmass storage device 1007. Mass storage device 1007 represents apersistent data storage device such as a floppy disc drive or a fixeddisc drive, which may be local or remote in some embodiments. Memory1003 may include read only memory, random access memory, etc.Applications resident on the computing device may be stored on oraccessed via a computer readable medium such as memory 1003 or massstorage device 1007 in some embodiments. Applications may also be in theform of modulated electronic signals modulated accessed via a networkmodem or other network interface of the computing device. It should beappreciated that CPU 1001 may be embodied in a general-purposeprocessor, a special purpose processor, or a specially programmed logicdevice in some embodiments.

Display 1011 is in communication with CPU 1001, memory 1003, and massstorage device 1007, through bus 1005. Display 1011 is configured todisplay any visualization tools or reports associated with the systemdescribed herein. Input/output device 1009 is coupled to bus 1005 inorder to communicate information in command selections to CPU 1001. Itshould be appreciated that data to and from external devices may becommunicated through the input/output device 1009. CPU 1001 can bedefined to execute the functionality described herein to enable thefunctionality described with reference to FIGS. 1-9. The code embodyingthis functionality may be stored within memory 1003 or mass storagedevice 1007 for execution by a processor such as CPU 1001 in someembodiments. The operating system on the computing device may be MSDOS™, MS-WINDOWS™, OS/2™, LINUX™, or other known operating systems. Itshould be appreciated that the embodiments described herein may also beintegrated with a virtualized computing system implemented with physicalcomputing resources.

Detailed illustrative embodiments are disclosed herein. However,specific functional details disclosed herein are merely representativefor purposes of describing embodiments. Embodiments may, however, beembodied in many alternate forms and should not be construed as limitedto only the embodiments set forth herein.

It should be understood that although the terms first, second, etc. maybe used herein to describe various steps or calculations, these steps orcalculations should not be limited by these terms. These terms are onlyused to distinguish one step or calculation from another. For example, afirst calculation could be termed a second calculation, and, similarly,a second step could be termed a first step, without departing from thescope of this disclosure. As used herein, the term “and/or” and the “/”symbol includes any and all combinations of one or more of theassociated listed items.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”,“comprising”, “includes”, and/or “including”, when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. Therefore, the terminology usedherein is for the purpose of describing particular embodiments only andis not intended to be limiting.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

With the above embodiments in mind, it should be understood that theembodiments might employ various computer-implemented operationsinvolving data stored in computer systems. These operations are thoserequiring physical manipulation of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated. Further, the manipulationsperformed are often referred to in terms, such as producing,identifying, determining, or comparing. Any of the operations describedherein that form part of the embodiments are useful machine operations.The embodiments also relate to a device or an apparatus for performingthese operations. The apparatus can be specially constructed for therequired purpose, or the apparatus can be a general-purpose computerselectively activated or configured by a computer program stored in thecomputer. In particular, various general-purpose machines can be usedwith computer programs written in accordance with the teachings herein,or it may be more convenient to construct a more specialized apparatusto perform the required operations.

A module, an application, a layer, an agent or other method-operableentity could be implemented as hardware, firmware, or a processorexecuting software, or combinations thereof. It should be appreciatedthat, where a software-based embodiment is disclosed herein, thesoftware can be embodied in a physical machine such as a controller. Forexample, a controller could include a first module and a second module.A controller could be configured to perform various actions, e.g., of amethod, an application, a layer or an agent.

The embodiments can also be embodied as computer readable code on atangible non-transitory computer readable medium. The computer readablemedium is any data storage device that can store data, which can bethereafter read by a computer system. Examples of the computer readablemedium include hard drives, network attached storage (NAS), read-onlymemory, random-access memory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes,and other optical and non-optical data storage devices. The computerreadable medium can also be distributed over a network coupled computersystem so that the computer readable code is stored and executed in adistributed fashion. Embodiments described herein may be practiced withvarious computer system configurations including hand-held devices,tablets, microprocessor systems, microprocessor-based or programmableconsumer electronics, minicomputers, mainframe computers and the like.The embodiments can also be practiced in distributed computingenvironments where tasks are performed by remote processing devices thatare linked through a wire-based or wireless network.

Although the method operations were described in a specific order, itshould be understood that other operations may be performed in betweendescribed operations, described operations may be adjusted so that theyoccur at slightly different times or the described operations may bedistributed in a system which allows the occurrence of the processingoperations at various intervals associated with the processing.

In various embodiments, one or more portions of the methods andmechanisms described herein may form part of a cloud-computingenvironment. In such embodiments, resources may be provided over theInternet as services according to one or more various models. Suchmodels may include Infrastructure as a Service (IaaS), Platform as aService (PaaS), and Software as a Service (SaaS). In IaaS, computerinfrastructure is delivered as a service. In such a case, the computingequipment is generally owned and operated by the service provider. Inthe PaaS model, software tools and underlying equipment used bydevelopers to develop software solutions may be provided as a serviceand hosted by the service provider. SaaS typically includes a serviceprovider licensing software as a service on demand. The service providermay host the software, or may deploy the software to a customer for agiven period of time. Numerous combinations of the above models arepossible and are contemplated.

Various units, circuits, or other components may be described or claimedas “configured to” or “configurable to” perform a task or tasks. In suchcontexts, the phrase “configured to” or “configurable to” is used toconnote structure by indicating that the units/circuits/componentsinclude structure (e.g., circuitry) that performs the task or tasksduring operation. As such, the unit/circuit/component can be said to beconfigured to perform the task, or configurable to perform the task,even when the specified unit/circuit/component is not currentlyoperational (e.g., is not on). The units/circuits/components used withthe “configured to” or “configurable to” language include hardware—forexample, circuits, memory storing program instructions executable toimplement the operation, etc. Reciting that a unit/circuit/component is“configured to” perform one or more tasks, or is “configurable to”perform one or more tasks, is expressly intended not to invoke 35 U.S.C.112, sixth paragraph, for that unit/circuit/component. Additionally,“configured to” or “configurable to” can include generic structure(e.g., generic circuitry) that is manipulated by software and/orfirmware (e.g., an FPGA or a general-purpose processor executingsoftware) to operate in manner that is capable of performing the task(s)at issue. “Configured to” may also include adapting a manufacturingprocess (e.g., a semiconductor fabrication facility) to fabricatedevices (e.g., integrated circuits) that are adapted to implement orperform one or more tasks. “Configurable to” is expressly intended notto apply to blank media, an unprogrammed processor or unprogrammedgeneric computer, or an unprogrammed programmable logic device,programmable gate array, or other unprogrammed device, unlessaccompanied by programmed media that confers the ability to theunprogrammed device to be configured to perform the disclosedfunction(s).

The foregoing description, for the purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the embodiments and its practical applications, to therebyenable others skilled in the art to best utilize the embodiments andvarious modifications as may be suited to the particular usecontemplated. Accordingly, the present embodiments are to be consideredas illustrative and not restrictive, and the invention is not to belimited to the details given herein, but may be modified within thescope and equivalents of the appended claims.

What is claimed is:
 1. A method, comprising: sending, by a secondstorage node, a second packet from the second storage node through astateless load balancer to a client, responsive to the second storagenode receiving a first packet associated with a stateful connectionassociated with a first storage node, and the second storage nodefailing to recognize the first packet associated with the statefulconnection; and sending further packets from the stateless load balancerto a plurality of storage nodes of the storage cluster, responsive toreceiving, at the stateless load balancer, the second packet from thesecond storage node, wherein the plurality of storage nodes resetstateful connection information responsive to receiving the furtherpackets.
 2. The method of claim 1, further comprising: trapping thesecond packet from the second storage node at the stateless loadbalancer, wherein the sending the further packets is responsive to thetrapping the second packet.
 3. The method of claim 1, wherein thesending the further packets from the stateless load balancer to theplurality of storage nodes comprises sending the further packets fromthe stateless load balancer to all of the storage nodes of the storagecluster except the second storage node.
 4. The method of claim 1,further comprising: updating a table in the stateless load balancer,responsive to adding a further storage node, wherein the first packetassociated with the stateful connection between the client and the firststorage node is received at the second storage node as a result of theupdating the table.
 5. The method of claim 1, wherein the sending thefurther packets comprises sending the further packets as out of bandcontrol packets.
 6. The method of claim 1, further comprising: injectinga packet to a kernel, in each of the plurality of storage nodes,responsive to receiving the further packets.
 7. The method of claim 1,wherein the sending the further packets from the stateless load balancerto the plurality of storage nodes comprises: sending a first pluralityof packets from a first stateless load balancer to a plurality of secondstateless load balancers each associated with one of a plurality ofchassis and sending a second plurality of reset packets from each of theplurality of second stateless load balancers to a subset of storagenodes in the chassis associated with the second load balancer.
 8. Atangible, non-transitory, computer-readable media having instructionsthereupon which, when executed by a processor, cause the processor toperform a method comprising: sending, by a second storage node, a secondpacket from the second storage node through a stateless load balancer toa client, responsive to the second storage node receiving a first packetassociated with a stateful connection associated with a first storagenode, and the second storage node failing to recognize the first packetassociated with the stateful connection; and sending further packetsfrom the stateless load balancer to a plurality of storage nodes of thestorage cluster, responsive to receiving, at the stateless loadbalancer, the second packet from the second storage node, wherein theplurality of storage nodes reset stateful connection informationresponsive to receiving the further packets.
 9. The computer-readablemedia of claim 8, wherein the sending the further packets from thestateless load balancer to the plurality of storage nodes comprisessending a further packet from the stateless load balancer to each of thestorage nodes of the storage cluster but not to the second storage node.10. The computer-readable media of claim 8, wherein the method furthercomprises: updating a table in the stateless load balancer, responsiveto removing a storage node, wherein the table records paths to storagenodes present in the storage cluster for distribution of packets by thestateless load balancer, and wherein the packet belonging to thestateful connection is received at the second storage node as a resultof the updating the table.
 11. The computer-readable media of claim 8,wherein the sending the further packets comprises sending out of bandreset packets.
 12. The computer-readable media of claim 8, wherein themethod further comprises: injecting a packet to a kernel, by an agent ineach of the plurality of storage nodes, responsive to receiving thefurther packet, wherein the injected packet is sized to a window inaccordance with packet monitoring by the agent, and wherein the statefulconnection is a transmission control protocol (TCP) connection and thereset packet is a TCP reset packet.
 13. The computer-readable media ofclaim 8, wherein the sending the further reset packets from thestateless load balancer to the plurality of storage nodes comprises:sending a first plurality of packets from a first stateless loadbalancer configurable to load balance across a plurality of chassis eachhaving a subset of storage nodes of the storage cluster, to each of theplurality of chassis and sending a second plurality of packets from asecond stateless load balancer of each of the plurality of chassis. 14.A storage cluster, comprising: a plurality of storage nodes, each havingone or more processors; storage memory, distributed across the storagecluster; a stateless load balancer, configurable to load balance packetsacross the plurality of storage nodes without tracking connectionstates; each of the plurality of storage nodes configurable to transmit,by the storage node, a first packet through the stateless load balancer,responsive to the storage node receiving a packet associated with astateful connection and the storage node failing to recognize the packetassociated with the stateful connection, wherein the stateful connectionis reset responsive to receiving the first packet; the stateless loadbalancer configurable to send further packets to a subset of theplurality of storage nodes, responsive to receiving the first packetfrom one of the plurality of storage nodes; and each of the plurality ofstorage nodes configurable to reset stateful connection informationresponsive to receiving one of the further packets.
 15. The storagecluster of claim 14, further comprising: the stateless load balancerconfigurable to trap the first packet from the one of the plurality ofstorage nodes, triggering the further packets.
 16. The storage clusterof claim 14, wherein the subset of the plurality of storage nodescomprises all of the plurality of storage nodes except the one of theplurality of storage nodes from which the first packet is received bythe stateless load balancer.
 17. The storage cluster of claim 14,further comprising: the stateless load balancer configurable to maintaina table having paths to the plurality of storage nodes, update the tableresponsive to adding a storage node or removing a storage node relativeto the cluster, and distribute packets in a manner in accordance withthe table for load-balancing, wherein the failing to recognize thepacket is a consequence of such a table update.
 18. The storage clusterof claim 14, wherein the first packet and each of the further packets isan out of band control packet, and wherein the stateful connection is atransmission control protocol (TCP) connection and the first packet is aTCP reset packet.
 19. The storage cluster of claim 14, furthercomprising: each of the plurality of storage nodes configurable to havean agent inject a packet to a kernel of the storage node, responsive toreceiving one of the further packets.
 20. The storage cluster of claim14, wherein the stateless load balancer comprises: a first statelessload balancer and a plurality of second stateless load balancers; thefirst stateless load balancer configurable to load balance across theplurality of second stateless load balancers; and each of the pluralityof second stateless load balancers associated with a chassis having asubset of storage nodes of the storage cluster and configurable to loadbalance across the subset of storage nodes.